Sperm cells multiple by __________.

Which of the following BEST illustrates a safety guideline for handling ladders?

A. Ladders may not be raised within 35 feet (11 m) of electrical wires or equipment. B. Firefighters should wear a full body harness and safety line when training on ladders. C. Firefighters should minimize training on ladders to reduce the chance of personal injury. D. Ladders should never be tied to structures or any other object that may restrict their movement.

The skin condition called ________ is caused by parasitic lice and is associated with overcrowded conditions and often with poor hygiene. 

Fill in the blank(s) with the appropriate word(s).