How should an analyst use the field calculator to concatenate fields “City_Name” and “Region” with a comma and a space between the values?

How should an analyst use the field calculator to concatenate fields “City_Name” and “Region” with a comma and a space between the values?
A . !City_Name! + “,” + !Region!
B . !City_Name! + “” + !Region!
C . !City_Name! + “,_” + !Region!
D . !City_Name! + “+” + !Region!

Answer: A