______, a fluid secreted by new mothers during the initial days of lactation, contains nutrients that boost a baby's immune system and helps fight infection.

Colostrum

The correct answer is Option (3)- Colostrum

The correct answer is "Colostrum."

Colostrum is a specialized fluid secreted by new mothers during the initial days of lactation, typically within the first few days after giving birth. It is rich in nutrients and antibodies that provide numerous health benefits to newborns.

Here's an explanation of each option:

1. Sebum: Sebum is an oily substance produced by the sebaceous glands in the skin, helping to moisturize and protect the skin and hair.
2. Synovia: Synovia, also known as synovial fluid, is a lubricating fluid found in joints, providing cushioning and reducing friction between the articulating surfaces of bones.
3. Colostrum: As mentioned earlier, colostrum is the initial milk produced by the mammary glands of mammals after giving birth. It contains high levels of antibodies, proteins, vitamins, and minerals, which help boost the baby's immune system and provide essential nutrients.
4. Cerumen: Cerumen, commonly known as earwax, is a waxy substance produced by glands in the ear canal. It helps protect the ear canal by trapping dust, dirt, and other foreign particles, preventing them from reaching the eardrum.

Therefore, colostrum is the fluid secreted by new mothers that contains nutrients to boost a baby's immune system and help fight infection.