What are the highest points on a standing wave called?
a. nodes
b. antinodes
c. compressions
d. rarefactions

B is the answer.

Standing waves have zero points called nodes, and points of maximum amplitude called antinodes.

Standing waves patterns are produced when two waves of the same frequency interfere with one another while travelling opposite directions along the same medium.

Standing waves patterns are characterized by certain fixed points along the medium which undergo no displacement. . These points are called nodes and are always located at the same location along  the medium giving the entire pattern an appearance of standing still. 

the answer is b

b. the carbon cycle ensures living things have a source of hydrogen

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)