When I was a child, I ……to school everyday instead going by cycle. A. had walked B. walked C. have walked D. have been walking

The correct answer is B. walked.

The sentence is in the past simple tense, which is used to talk about things that happened in the past and are not happening now. The other options are not in the past simple tense.

• Had walked is in the past perfect tense, which is used to talk about things that happened before another event in the past.
• Have walked is in the present perfect tense, which is used to talk about things that have happened up to now.
• Have been walking is in the present perfect continuous tense, which is used to talk about things that have been happening for a period of time and are still happening.

In this case, the speaker is talking about something that happened in the past and is not happening now, so the past simple tense is the correct tense to use.