Question

Read the statements and click an appropriate verb option. Active Past or Present Continuous forms.
Tom (was assisting, assisted,are assisting) the doctors in Africa for a few months.
When Ann was a volunteer in Brazil, she (tested, tests, was testing) the soil for harmful elements.
Doctors from this hospital (are sharing, are shared, shared) their experience with colleagues from other countries now.

Answer 1

Tom was assisting the doctors in Africa for a few months. (for a few month -- маркер Past Continuous)

When Ann was a volunteer in Brazil, she was testing the soil for harmful elements. (действие длилось,Past Continuous)

Doctors from this hospital are sharing their experience with colleagues from other countries now. (now -- маркер Present Continuous)

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Past Continuous -- was/were + V-ing

Present Continuous -- am/is/are + V-ing