The recommended weight limit according to NIOSH would be base on an equation and is dependent to a number of factors. This equation is called the NIOSH Lifting equation. Under ideal conditions, the maximum recommended weight is 51 pounds. Hope this answers the question.
The answer is C but if it is wrong then the answer is B
I believe it is metaphor, but i am not a 100% sure
The answer is D) the more benefit they will recieve from exercise