Read the given statements and conclusions carefully. You have to take the given statements to be true even if they seem to be at variance from commonly known facts and decide which conclusion(s) logically follow(s) from the given statements.
Statements:
Some kings are servants.
Some servants are fighters.
Conclusions:
(I) Some fighters are kings.
(II) All servants are kings.

​Statements:
Some kings are servants.
Some servants are fighters.

​​Conclusions:

Some fighters are kings. (False, there is no direct relation between fighters and kings).
All servants are kings. (False, there can be some servants who are not kings, so this conclusion is also incorrect).

Thus, correct option is (a).