Question

join each pair of sentences using the present perfect continuous
Mary is working in London
she started working there on 18 Jan
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Answer 1

In this particular sentence, the blank defines a something that started in the past and is still continuing which is why we would be using the present perfect continuous tense. It (also known as the present perfect progressive tense) shows that something started in the past and is continuing at the present time.

The present perfect continuous is formed using the construction:

has/have been + the present participle (root + -ing)

Option C is the correct form, the sentence being in third person there is usage of "has" followed by the present participle (Root+ing)

Option A is an example of present perfect tense

Option B and D is an example of present and past continuous tense

Option C is correct