Answer:
OA. It's a federal offense to open another person's mail without permission.
Step-by-step explanation:
The term "federal" can be used in two ways- be it with a capitalized "F" or a small letter "f". The use of capital and small letter depends on the use of the word.
For instance, if we are talking about a proper noun like the Federal law, or a name of a federal agency, the capital "F" should be used. But if that is not the case, then there is no need to capitalize the "f" every time.
So, in the given sentence, it is talking about a crime, an offense. So, the term "federal" will be in small letters.
Thus, the correct answer is option A.