The protein- and antibody-rich milk a mother secretes after giving birth is called
a. colostrum
b. estrus
c. parturition
d. gravid

The correct answer is A.

Colostrum is a milky substance that is produced by the breasts of mammals before birth and during the first few days following birth.

Colostrum precedes the production of true milk, or breast milk. It is usually clear in appearance but may look yellow or white.

It is rich in proteins, carbohydrates, fats, vitamins, minerals and antibodies. The antibody level on colostrum can be as high as 100 times the level found in regular cow's milk. 

The digestive system plays one of the major functions of the body. Without it, you couldn't be able to get the nutrients you need to grow properly and stay healthy. It is very important for breaking down food into nutrients, which the body uses for energy, growth, and cell repair. Foods and drinks must be changed into smaller molecules of nutrients before the blood absorbs them and carries them to cells throughout the body.