All of the following protect the skin and mucous membranes from infection except
a) multiple layers of cells.
b) tears.
c) saliva.
d) hcl.
e) the "ciliary escalator."

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.

a=c and then d= c because of the band so you get ac/dc and you add them together you get sound waves