Monocytes
Macrophages
Immunoglobulin A
Natural killer cells
Correct option is Immunoglobulin A. Colostrum, the yellowish fluid secreted by the mother during initial days of lactation is very essential to impart immunity to the new born infant because it contains immunoglobulin A. It will impart naturally acquired passive immunity to the new-born. So, the correct answer is 'Immunoglobin A'