Почему пишется с is, и какое это время? lesson is over

Есть устойчивое выражение to be over.

Переводится: заканчиваться.

Is---форма глагола to be в третьем лице единственного числа. Когда мы говорим урок окончен, урок это третье лицо , поэтому и ставится форма глагола is

Much was done by people to reach the present state of human development. it is necessary to say that great contribution to the development of the world science and culture, literature, music and painting was made by the russian people. the names of russian scientists and writers, poets, composers and painters are world-famous-pushkin, lermontov, chehov, levitan. this chain can be endless. it is almost impossible to name a branch of science in the development of which the russian scientists havent played the greatest role. lomonosov, the founder of the moscow university was an outstanding innovator both in the humanities and sciences. mendeleevs greatest discovery was the periodic system of elements. popov invented radio. sechenov and pavlov were the worlds greatest physiologists. russia is rightly called the mother of aviation and cosmounatics. names of tsiolkovsky, korolov and gagarin are symbols of new space era.  держи)