Which Of these formula can combine two cell's content into one cell? A- Sum() B- Concatenate() c- N()?

It's (b) "concatenate" is the correct answer.

The Answer is B: Concatenate.

& Operator

=concatenate() function

but try asap utilities.

We can also use & function to add or merger two cells.

Select the cell in which you want to combine the contents of other cell

1. To start the formula, type =(

2.  select the first cell that contains the text that you want to combine, type&" "&  and then select the next cell that contains the text that you want to combine.
3. To insert a comma, type &", "& 
4. then enter

Concatenate() function in the one.

but now with Excel 2016 there is a better function called 

TEXTJOIN()

B- Concatenate it the Right Answer ..

and you can use the "&" Operator to combine text in one cell