Read these sentences and choose the correct answer to fill in the gaps. 1. That's ridiculous- you be joking.

can
must

2. It be the postman; it's far too early.

mustn't
can't

3. I do my homework.

Correct answer 1:  must

Correct answer 2:  can't

Correct answer 3:  must

Объяснение:

Modal verb 'can'

Can is an auxiliary verb, a modal auxiliary verb. We use can to:

- talk about possibility and ability

- make requests

- ask for or give permission

The main verb is always the bare infinitive (infinitive without "to").

subject

auxiliary verb

main verb

+

I

can

play

tennis.

-

He

cannot/can't

play

tennis.

?

Can

you

play

tennis.

Modal verb 'must'

We often use must to say that something is essential or necessary, for example:

 

Must is a modal auxiliary verb. It is followed by a main verb.

subject

auxiliary verb

main verb

I

must

go

home.

You

must

visit

us.

We

must

stop

now.

In general, must expresses personal obligation. Must expresses what the speaker thinks is necessary. Must is subjective.

In each of the above cases, the "obligation" is the opinion or idea of the person speaking. In fact, it is not a real obligation. It is not imposed from outside.

Dear sir!   i have found this catalonia cathedral hotel in the internet. i'd like to book a room for three people with one extra bed for a 12 years child from 23 june till   3 july.   maybe you have full board or all inclusive service. also we'd like to have a terrace with a swimming pool and wonderfull view on gotic cvartal of barcelona. maybe you'll be able to give us   a 10% discount for 10 days reservation.    please, answer as sonn as possible.