The most likely answer would be C if the topic is toddlers.
HOWEVER if their is no information to support that it is about toddlers in your marital then it is most likely D.
The error in this sentence is a A) pronoun-antecedent voice agreement error. But it should be noted that this has become more standard usage in common dialogue.
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.
