What is the major obstacle in developing good human relations skills?
a. human relations aren't rewarding.
b. common interests won't to keep a conversation going.
c. people fear taking risks.

There are several reasons why there are obstacles in developing human relation skills. A major obstacle is that common interests won't help keep a conversation going. There will be silences in the conversation and this can become awkward. The correct answer is B. 

Molecules called lipids have long hydrocarbon chains that determine the way they act. they can be fats, oils, or hormones, and even exist in our cell membranes 

It's either -limiting factors or -scarce resources but i'd go with my first answer since the food and water are abundant they really aren't scarce