Answer:
The weakness in the sentence is the following one:
A. It attempts to be humorous.
Step-by-step explanation:
It is a cover letter, and as so it is supposed and expected to have a serious, formal tone, since it has to do with work. Trying to be funny on a cover letter is as inappropriate as bursting out laughing at a funeral service. A cover letter is an introduction to someone's CV, and it is sent with other documents that prove one's qualifications. Therefore, attempting to be humorous on a cover letter sounds naive and childish, and whoever writes a cover letter wants to be taken seriously.