What is a possible explanation for the "jump" in stan's length at 3 months of age?

Three months of age is a typical time for a major growth spurt. Gaining weight, growing in length are common at this age. He may begin eating a lot more as well.

The possible explanation for the "jump" in stan's length at the age of 3 months may be because of genetics. Genetics is defined as the study of genes, heredity in living organism and genetic variation. In human beings, according to the expects, it is estimated that there are 60,000 to 100,000 genes (made up of DNA) 46 chromosomes. 

The answer is d. when it begins to fall back to the child's hand