Question

How long had you been owning/owned the flat before you sold it?My shoes were dirty because I had been working/I had worked in the garden?

Answer 1

Answer:

How long had you owned the flat before you sold it?

My shoes were dirty because I had worked in the garden?

Explanation:

The past perfect tense also known as the pluperfect is used to refer to an action or event that occurred before a specified time in the past. It is formed by combining 'had' with the past participle or past tense of the main verb. In the two sentences above, the correct tenses are;

had you owned, and

had worked.

The events happened before a specific time in the past. For example, The first subject owned a flat in the past, before he sold it. The ownership as well as the sale were both past events.