Weight training has the biggest effect on
a. cardiac muscles
b. smooth muscles
c. involuntary muscles
d. skeletal muscles

d. skeletal muscles

Weight training has the biggest effect on the skeletal muscles. When a person is engaged in weight training activities the skeletal muscles are forced to move beyond their comfort zone because of the added weight. As a result, muscle fibers develop micro-tears. These micro-tears when they regenerate through time increases the number of muscle fibers and the size of the fibers themselves. 

Maybe haha