Directions: Read the following sentences (A, B, C, and D) and determine which of these sentences is/are grammatically and contextually correct.

A. Each of the participants were required to submit a detailed report on the project.

B. Significant changes in the climate patterns have been observed over the past decade, affecting even the most resilient ecosystems.

C. His ability to articulate complex concepts clearly makes him a valuable asset to the team.

D. The book's protagonist, despite facing numerous challenges, manage to overcome them all by the story's end.