Choose the tense: Present /Past /Future Simple; Present/ Past /Future Continuous; Present/ Past /Future Perfect; Present/ Past /Future perfect Continuous
1. Где ты был вчера? 
2. Я работаю над этой проблемой уже три месяца.
3. Три месяца назад я работал над этой проблемой.
4. Я работал над этой проблемой с 3 до 5 вечера.
5. Он всегда работает хорошо.
6. Завтра он будет работать над этой проблемой.
7. Завтра в три часа ночи они будут работать над этой проблемой.
8. Завтра к трем часам они закончат работать над этой проблемой.
9. На следующей неделе к трем часам он уже переведет половину статьи.

1. Where were you yesterday?
2.I've been working on this problem for three months
3.Three months ago, i was working on this problem.
4.I worked on this problem from 3 to 5 pm
5/On always works well.
6. Tomorrow he will be working on the problem.
7. Tomorrow at three in the morning they will be working on the problem.
8. Tomorrow at three o'clock they finish work on the problem.
9. The following week, at three o'clock he will transfer half of the article.


И в таком варианте
1. Where were you yesterday?
2. I work on this problem already three months.
3. Three months back I worked on this problem.
4. I worked on this problem from 3 to 5 evening.
5. He always works well.
6. Tomorrow he will work on this problem.
7. Tomorrow at three o'clock of night they will work on this problem.
8. Tomorrow to three hours they will finish to work on this problem.
9. Next week to three hours he will translate the half of the article already.