You should be aware . . . . . . . . your faults. A. by B. in C. of D. on

The correct answer is C. of.

The preposition “of” is used to indicate possession or association. In this case, it is used to indicate that you should be aware of your faults. This means that you should be aware of the things that you do wrong, and you should try to improve on them.

The other options are not correct because they do not convey the same meaning.

• The preposition “by” is used to indicate a means or method. In this case, it would not make sense to say that you should be aware of your faults by something.
• The preposition “in” is used to indicate a location or position. In this case, it would not make sense to say that you should be aware of your faults in something.
• The preposition “on” is used to indicate a surface or location. In this case, it would not make sense to say that you should be aware of your faults on something.