I.

1. My friend comes from Australia. - Pr.S.

My friend came ... last year. - P.S.

My friend is coming ... this summer. - Pr.C.

My friend was coming ... while I was waiting for her in my home country. - P.C.

My friend had come to Russia from Australia before I came there. - P.P.

My friend hasn't come yet.- Pr.P.

2. We buy English magazines. - Pr.S.

We bought ... last week. - P.S.

We are buying ... now. - Pr.C.

We were buying ... while you were standing outside.- P.C.

Before you got these books, we had bought ... .- P.P.

We have bought ... already. - Pr.P.

3. He spoke about it last time. - P.S.

He always speaks about it. - Pr.S.

He is speaking about it at the moment. - Pr.C.

He was speaking about it yesterday during the lunch. - P.C.

He had spoken about it before we came. - P.P.

He has spoken about it recently. - Pr.P.

4. They have many questions to ask you. - Pr.S.

Yesterday they had many questions to ask you. - P.S.

They had had many questions to ask you even before you came. - P.P.

They have had many questions to ask you. - Pr.P.

времена с continuous в данном контексте кажутся мне не очень уместными, но пусть будет:

They are having many questions to ask you right now. - Pr.C.

They were having many questions to ask you during yesterday's concert. - P.C.

5. The word "hamburger" comes from the name of German city Hamburg. - Pr.S.

The word "hamburger" came ... in 1900. - P.S.

The word "hamburger" had come ... before the first American restaurant serving it was opened. - P.P.

The word "hamburger" has come ... .

опять же, контекст, я думаю, не допускает использования времен с continuous. на этот раз это просто не будет звучать.

The word is coming ... . - Pr.C.

The word was coming ... . - P.C.

II.

1. Her aunt works on Saturdays. - Pr.S.

Her aunt worked last Saturday. - P.S.

Her aunt is working this weekend. - Pr.C.

Her aunt was working for this company from 2 to 4 o'clock yestersday. - P.C.

Her aunt had worked here before her uncle was hired. - P.P.

Her aunt has worked here. - Pr.P.

2. см. выше

3. Alex is an economist. - Pr.S.

Alex was an economist. - P.S.

тут уже точно не употребить continuous, т.к. be - это глагол состояния

When Greg graduated from school, Alex had been an economist already. - P.P.

Alex has been an economist. - Pr.P. (так же сомневаюсь, допустимо ли вообще употребление времени в данном контексте)

4. She usually has lunch at two. - Pr.S.

She had lunch at two. - P.S.

She is having lunch now. - Pr.C.

She was having lunch during the break. - P.C.

She had had lunch already before the bell rang. - P.P.

She just has had lunch. - Pr.P.

5. см. выше

фух. надеюсь, грубых ошибок не допустила. если что, отвечу на любые вопросы (: