make for：导致;有利于 If something makes for another thing, it causes or helps to cause that thing to happen or exist.
如：A happy parent makes for a happy child.有快乐的父母,才会有快乐的孩子.
add to：.增添；增加 If one thing adds to another, it makes the other thing greater in degree or amount.
如：Smiles, nods, and cheerful faces added to the general gaiety.
微笑、点头和喜洋洋的脸庞使喜庆的气氛变得更浓了.
Her comments will add to the uncertainty of the situation. 她的批评将会使局势更加不稳定.
这题填add to,意指增加节日气氛.