Which set of words indicates that the author is demonstrating the cause and effect of events?

A. So; because; therefore; as a result
B. Above; behind; next to; below ***
C. Help; problem; obstruction; difficulty
D. Principal; central; fundamental; instrumental

No, sorry.

Is it C

No. You've guessed wrong twice now. No more will be checked.

http://grammar.ccc.commnet.edu/grammar/composition/cause_effect.htm
Read all this and think carefully before you choose again.

The set of words that indicates that the author is demonstrating the cause and effect of events is A. So; because; therefore; as a result.

To identify cause and effect in a passage, you can look for words or phrases that suggest a causal relationship between events. In this case, the words "because" and "therefore" explicitly show a cause and effect relationship. The word "so" can also indicate a cause and effect relationship when used in the context of explaining a result or consequence. Similarly, the phrase "as a result" implies that one event is directly causing another event. By analyzing the usage of these words and phrases, you can determine whether the author is explaining cause and effect.