Question

acne
a is caused by a bacterial infection.
b is caused by low levels of sebum.
c affects all teenagers.
d all of the above

Explanation:

Acne is often caused by a bacterial infection (Propionibacterium acnes) that thrives in clogged hair - follicles. High, not low, sebum levels contribute to acne as excess sebum can clog pores. Not all teenagers get acne as it depends on various factors like genetics, diet, and skincare.

Answer:

A. is caused by a bacterial infection