Answer:
immature immune system
Explanation:
Colic is a condition where an infant cries for unknown reasons. Generally infant cries when they are hungry or needs diaper change or has some other problems. But it is seen that those babies who are well taken care off and are well feed also cries non stop for unknown reason.
Such babies are said to have been suffering colics. It is caused by unknown germs that causes pain in their stomach. Babies with colics may be allergic to milk. Babies have immature immune systems which causes colics
Colics are harmless and they last for the first few months ranging from 1 month to the 5 month.
Thus the answer is immature immune system.