Answer:
D. Trying to master one virtue at a time.
Step-by-step explanation:
The usage of metaphors is a common technique for the authors to elaborate, illustrate and emphasize their message more effectively. Similarly, here also the author employs the metaphor of weeds to exemplify the intended qualities that he feels of himself and suggests that one should pursue and master one virtue at a time. He says that if someone has a garden to weed(bad habits or deeds to rectify), it doesn't imply that one would eradicate all the bad herb(follies) at one time. But rather one should go step by step to eradicate these evils. Thus, this comparison illustrates his attempt to master one virtue at a time.