Why should you avoid typing in all capital letters?
a. it is interpreted as yelling.
b. it is difficult to read.
c. it is insulting to others.
d. only acronyms should be in all capital letters.

A, Typing all capital letters conveys a strong sense of emotion or urgency to the reader. This emphasis is not nesscary all the time and can be considered annoying. In addition capital letters often hold significance (like you said an example would be acronyms) and it can be harder to differentiate  meaning if everything is always capitalized.  

Lake Powell, formed by Glen Canyon Dam,is not a lake.It is a reservoir, with a constantly fluctuating water level--more like a bathtub that is never drained than a true lake.