Although testosterone and related steroids clearly increase muscle mass during puberty, it has been more difficult to determine scientifically whether adult men with normal testosterone can get stronger from extra steroids, partly because:

It is unethical.

Explanation:

Testosterone is the important hormone that plays an important role in the development of male development and steroids are also involved in the proper development of an individual.

These  testosterone and related steroids increase muscle mass during puberty. This is difficult to determine testosterone can get stronger from extra steroids because this is against the ethics research. This can be used by the athletes to improve their performance.

i am positive it is c. condensing but i may be wrong

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)