Answer:
D). They were informed earlier about Mr. Taft’s plan.
Step-by-step explanation:
The watchman retreated as they had been informed previously about Mr. Taft's plan. The evidence to this claim is provided within the sentence as it says "wisely retreated" and "it was in the plan for them to retreat" that clearly portrays the purpose of watchman and Mr. Taft to withdraw their boat "before so overwhelming a force". Thus, option D is the correct answer.