Muscles in animals are often found in pairs, because
a. muscles can only pull.
b. muscles need to be able to both push and pull.
c. muscles can only push.
d. muscles can only produce a force as they relax.

The correct answer is muscles can only pull.

The movement of arm takes place by the relaxation and contraction of muscles. Muscles in animals are in pair because muscles can only pull, when a pair of muscle is present in animals one muscle relaxes and the other one contracts. An example of this is biceps and triceps of arm. The triceps  of the arm relaxes while the biceps of the arm  contracts, this movement helps to lift the arm. The reverse also takes place in the arm.

children tend to take more after their grandparents more than their parents. it’s the dna you received that was passed down to you somewhere in your family. maybe one of your grandparents had/has straight hair and you might have gotten it from them.

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.

: -)