The correct answer is: C. visited
The other options are:
A. helped: This is not the correct answer because it is not the same as “called on”. To help someone means to do something for them, while to call on someone means to go to see them.
B. surrounded: This is not the correct answer because it is not the same as “called on”. To surround someone means to be all around them, while to call on someone means to go to see them.
D. criticised: This is not the correct answer because it is not the same as “called on”. To criticise someone means to say bad things about them, while to call on someone means to go to see them.
To “call on” someone means to go to see them, especially when they are ill. It is a way of showing support and concern.