4. connect the sentences with when or if to form the first conditional. jack will come. we shall play chess. — when jack comes, we shall play chess. all the pupils will come to school tomorrow. we shall write a test then. i’ll meet ann after school. i’ll give her my album. you’ll not do your homework. the teacher will be angry. mike won’t come today. we’ll play football without him. i’ll finish school with good marks. my father will take me to the seaside. my school record may not be very good. mom will be very upset.

When all the pupils come to school tomorrow, we shall write a test. when i meet ann after school, i’ll give her my album. if you do not do your homework, the teacher will be angry. if mike doesn’t come today, we’ll play football without him. if l finish school with good marks, my father will take me to the seaside. if my school record is not very good, mom will be very upset.

a  telephone, or  phone, is a  telecommunications  device that permits two or more users to conduct a conversation when they are too far apart to be heard directly. a telephone converts  sound, typically and most efficiently the  human voice, into electronic signals suitable for  transmission  via cables or other transmission media over long distances, and replays such signals simultaneously in audible form to its user.

in 1876, scottish emigrant  alexander graham bell  was the first to be granted a united states patent for a device that produced clearly intelligible replication of the human voice. this instrument was further developed by many others. the telephone was the first device in history that enabled people to talk directly with each other across large distances. telephones rapidly became indispensable to businesses, government, and households, and are today some of the most widely used  small appliances.

the essential elements of a telephone are a  microphone  (transmitter) to speak into and an  earphone  (receiver) which reproduces the voice in a distant location. in addition, most telephones contain a  ringer  which produces a  sound  to announce an incoming telephone call, and a dial or keypad used to enter a  telephone number  when initiating a call to another telephone. until approximately the 1970s most telephones used a  rotary dial, which was superseded by the modern  dtmf  push-button dial, first introduced to the public by  at& t  in 1963.  the receiver and transmitter are usually built into a  handset  which is held up to the ear and mouth during conversation. the dial may be located either on the handset, or on a base unit to which the handset is connected. the transmitter converts the  sound waves  to  electrical signals  which are sent through the telephone network to the receiving phone. the receiving telephone converts the signals into audible sound in the receiver, or sometimes a  loudspeaker. telephones permit  duplex communication, meaning they allow the people on both ends to talk simultaneously.

the first telephones were directly connected to each other from one customer's office or residence to another customer's location. being impractical beyond just a few customers, these systems were quickly replaced by manually operated centrally located switchboards. this gave rise to  landline  telephone service in which each telephone is connected by a pair of dedicated wires to a local central office switching system, which developed into fully automated systems starting in the early 1900s. for greater mobility, various radio systems were developed for transmission between mobile stations on ships and automobiles in the middle 20th century. hand-held  mobile phones  were introduced for personal service starting in 1973. by the late 1970s several mobile telephone networks operated around the world. in 1983, the  advanced mobile phone system  (amps) was launched, offering a standardized technology providing portability for users far beyond the personal residence or office. these analog cellular system evolved into digital networks with better security, greater capacity, better regional coverage, and lower cost. the  public switched telephone network, with its hierarchical system of many  switching centers, interconnects telephones around the world for communication with each other. with the standardized international numbering system,  e.164, each telephone line has an identifying  telephone number, that may be called from any authorized telephone on the network.

although originally designed for simple voice communications,  convergence  has enabled most modern cell phones to have many additional capabilities. they may be able to  record spoken messages, send and receive  text messages,  take and display photographs  or  video, play music or  games,  surf the internet, do  road navigation  or immerse the user in  virtual reality. since 1999, the trend for mobile phones is  smartphones  that integrate all mobile communication and computing needs.