The stenographer is very efficient. He is . . . . . . . to his firm.

a credit
a blessing
an asset
a boon

The correct answer is: C. an asset

An asset is something that is valuable or useful. In this case, the stenographer is very efficient, which means that he is valuable to his firm. He is able to do his job quickly and accurately, which saves the firm time and money. He is also able to take notes during meetings and conferences, which can be helpful for the firm in making decisions.

The other options are not as accurate. A credit is something that is given to someone, such as a loan. A blessing is something that is good or fortunate. A boon is a great advantage or benefit. While the stenographer may be all of these things, he is most accurately described as an asset.