Употребите предложения в Present Perfect или Past Simple 1. Students are cleaning their classrooms. (already, last Saturday 2. The teacher is explaining a new rule. (Just; at the previous lesson) 3. Ann is doing her homework now. (just; on Friday) 4. They are discussing this problem again. (many times; a few days ago) 5. Granny is making a birthday cake. (just, yesterday)

1. Students have already cleaned their classrooms last Saturday.
Explanation: "Already" is used to indicate that the action of cleaning the classrooms occurred before a particular point in the past, which in this case is last Saturday. Therefore, we use the Present Perfect tense.

2. The teacher has just explained a new rule at the previous lesson.
Explanation: "Just" is used to indicate that the action of explaining the new rule happened a very short time before now, in this case, at the previous lesson. Therefore, we use the Present Perfect tense.

3. Ann has just done her homework on Friday.
Explanation: "Just" is used to indicate that the action of doing her homework happened a very short time before now, in this case, on Friday. Therefore, we use the Present Perfect tense.

4. They discussed this problem many times a few days ago.
Explanation: "Many times" and "a few days ago" both indicate a specific past time when the action of discussing the problem repeatedly happened. Therefore, we use the Past Simple tense.

5. Granny has just made a birthday cake yesterday.
Explanation: "Just" is used to indicate that the action of making a birthday cake happened a very short time before now, in this case, yesterday. Therefore, we use the Present Perfect tense.