Answer:
A. "All I can say is that I am well"
Step-by-step explanation:
The informal style of writing is when we are familiar with the receiver and there is no need for any formality between the receiver and the sender. And with an informal style, the language used can be personal and free, with no restrictions on the use of casual words.
In the given letter written by US General Ulysses S. Grant, he used informal wordings in the line "All I can say is that I am well." This is a casual approach language that suggests that the receiver is someone the General is familiar and close with.
Thus, the correct answer is option A.