Whoever answers first gets brainli... Why do the birds wings move down when it flies?
A. The wings need to go down some of the time to reduce friction
B. The wings need to point in the direction of force of gravity
C. The wings move up to down to avoid the friction between the air and the wings.
D. The wings push down on the air to overcome gravity.

B

Explanation:

its d. you give me brainliest

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."