The correct answer is: E. magnanimous, eager.
A magnanimous person is generous and forgiving, while an eager person is enthusiastic and willing to do something. In this case, the person is so generous and forgiving that everyone is always eager to help him in his work.
The other options are not as good fits for the sentence. A helpful person is someone who is willing to help others, but this does not necessarily mean that they are eager to do so. An aloof person is someone who is distant and unapproachable, so it is unlikely that people would be eager to help them. An adamant person is someone who is determined and will not change their mind, which could make it difficult for others to help them. A miserly person is someone who is stingy with money or possessions, so it is unlikely that people would be eager to help them. An ignorant person is someone who lacks knowledge or understanding, so it is unlikely that people would be eager to help them.