Если мы хотим подчеркнуть, что нам не важно в какую пятницу что-то произошло, или мы не помним точной даты, но твердо уверены, что это было в «какой-то, один из» понедельник, то ставим артикль а: i bet we met on a monday, though i do not remember the date exactly. тогда почему во втором предложении стоит нулевой артикль? i met her on friday. я встретил ее в пятницу.

I dream of a school in which everyone would be happy, in which there would be no sadness and pain, and if there were, it would be only a little or only in order to understand joy better. Sometimes teachers swear at us, but it is not always deserved and it is not always pleasant to look at teachers who allow themselves excessive emotions, they may not look quite beautiful.

I dream of a school in which everyone would be happy, in which there would be no sadness and pain, and if there were, it would be only a little or only in order to understand joy better. Sometimes teachers swear at us, but it is not always deserved and it is not always pleasant to look at teachers who allow themselves excessive emotions, they may not look quite beautiful.Therefore, in the school of my dreams, only the ideal teachers. Only those who really know how to transfer knowledge to children and, most importantly, are able to make everyone feel comfortable and cozy in the classroom. It is difficult to study when there is noise in the classroom, a lot of swearing, when, in general, for the most part they only shout, I like calmness more when it is quiet in the classroom and you can only hear the rustle of the pages of books and notebooks, how chalk roughens the board, you can even hear a note slipping between the desks or a concentrated look looks at another.

1) Sally had been painting the house all day before she finished them.

Past Perfect Continuous, т.к. речь идет о действии в , которое длилось в течение какого-то определенного периода и завершилось каким-то результатом - Сэлли красила дом весь день (продолжительное действие) и закончила (результат).

2) Anthony had been waiting for his airplane for 3 hours when its delay was announced.

Past Perfect Continuous, т.к. речь идет о продолжительном действии в , которое уже совершалось какое-то время к тому моменту, как было совершено другое - Энтони уже ждал самолет 3 часа (продолжительное действие) к тому моменту, как его перенос был объявлен.

3) They had bought a car before the price increased.

Past Perfect, т.к. здесь нет продолжительного действия, одно действие предшествует другому, и так как последующее действие (the price increased) указано в простой форме (Past Simple), предшествующее ему должно быть использовано в Past Perfect.