1. 

ATTEMPT
A. Serve
B. Explore
C. Try
D. Explain

Answer: Option C

Explanation:

Meanings of the given words:

Attempt :  to try to do something, especially something difficult 
.

Serve means to help somebody, who are in needy or perform duty etc.


Explore : means to search or to discover something which is already present.


Try : make an attempt or effort to do something.


Explain: describe, give an explanation of.