Charles was born in 1959. his mother took the drug thalidomide for nausea during her pregnancy. as a result, charles was born with no hands. charles's mother must have taken the drug between 28 and 54 days after conception because this is a period for the development of the hands.

The answer is: Critical period

Explanation:

Thalidomide is an immunomodulatory drug, which is prescribed as a tranquilizer or hypnotic for insomnia, anxiety and gastritis.  

When administered by pregnant women during the first and the second trimester, this drug caused teratogenic deformities in the newborns.

The deformity caused depends majorly on how many days into the pregnancy the mother administered the drug. If the drug is taken up to day 28, it causes damage to the legs. This is because it is a critical period for the development of legs.

Critical period refers to the stage of development of the child. During this stage, the central nervous system is very sensitive to certain environmental stimuli.