The simplest way to gain weight is to a. exercise several hours a day. b. figure out where in your day you could eat more food. c. eat several protein bars each day. d. have egg-white omelets for breakfast.

A. exercise several hours a day.

Explanation:

For those who want to gain weight without accumulating excess fat, the key is to increase weight through gaining muscle mass. For this, it is necessary to practice physical exercises several hours a day that cause a great effort and muscle wear, such as weight training and crossfit, besides having a protein rich diet, such as meat and eggs.

In addition, in some cases protein supplements may be required to increase the stimulation of hypertrophy and accelerate muscle recovery after physical activity.

b) the heart is a pump made of muscle and that is difficult to grow in the lab.