I think e because a primary source is first hand so you know all the details about what's happening during that time.
Answer: the answer is on google
past tense: bogged; past participle: bogged
cause (a vehicle, person, or animal) to become stuck in mud or wet ground.
(of a person or process) be unable to make progress.
Explanation:
"the car became bogged down on the beach road"
"you must not get bogged down in detail"
Churchill believed an invasion of British soil is not likely to occur I. The near future because the British naval forces created a strong barrier in the ocean