is work done to keep equipment in good working order.

This question is incomplete; here is the complete question:

is work done to keep equipment in good working order.

A. Defragmentation

B. Preventive maintenance

C. Virus protection

D. A maintenance schedule

The correct answer is B. Preventive maintenance

Explanation:

Maintenance refers to the processes done on machinery or equipment to preserve its proper functioning. Moreover, this maintenance is preventive if it is done to prevent equipment from breaking down or having any malfunctioning. Besides this, preventive maintenance is globally recommended because in this way equipment used at home or in business works properly. According to this, the correct answer is preventive maintenance.

dna is made up of six smaller molecules -- a five carbon sugar called deoxyribose, a phosphate molecule and four different nitrogenous bases (adenine, thymine, cytosine and guanine).

cell division is not regulated in tumor cells.