Q1. The .......... is at its largest in children, but with the onset of puberty, it eventually shrinks and gets replaced by fat.
A Parathyroid gland
B Thymus Correct
C Hypothalamus
D Pituitary gland
Explanation
The thymus is largest during childhood and then undergoes involution after puberty, when much of its tissue is gradually replaced by fat. This fits the stem exactly. The parathyroid glands regulate calcium balance and do not show this characteristic large-childhood-to-fat-replacement pattern. The hypothalamus is a brain region that controls many endocrine and autonomic functions, not a gland that normally shrinks in this way at puberty. The pituitary gland is the master endocrine gland and remains functionally important after puberty; it is not the structure described by the question.