Ребята . . . . . . . . . . . .​

1) My friend came back from business trip yesterday. Our teacher has asked me twice today.

2) The plane has just landed. He gave me his notes last week.

3) She has sent three letters to this firm already. They did the exercises quickly yesterday.

4) The workers have gone to the meeting already. He asked many questions last lesson.

5) I have spoken with my boss already. They went to the seaside by train last summer.

Объяснение:

Past Simple Tense:

1) Действие закончилось в

2) Есть указатель времени в вчера, на неделе летом, в 2001 году и т.п.

Present Perfect:

1) Когда произошло действие неважно, важен результат: самолет приземлился, письма отправили, работники уже ушли.  

2) Отрезок времени не указан или еще не закончился: сегодня (сегодня еще не закончилось), на этой неделе (эта неделя еще продолжается), в этом году (этот год все еще продолжается) и т.п.

The simple past, past simple or past indefinite, sometimes called the preterite, is the basic form of the past tense in Modern English. It is used principally to describe events in the past, although it also has some other uses. Regular English verbs form the simple past in -ed; however, there are a few hundred irregular verbs with different forms.

The term "simple" is used to distinguish the syntactical construction whose basic form uses the plain past tense alone, from other past tense constructions which use auxiliaries in combination with participles, such as the past perfect and past progressive.