According to the Textbook, Which One of the Following Conclusions

According to the textbook, which one of the following conclusions is most warranted from research on brain development?

A) Classroom experiences can affect students' cognitive development throughout the elementary and secondary school years.
B) It is essential that children begin studying basic mathematics and science before the age of seven.
C) The ability to think abstractly depends on the development of many synaptic connections during the first five years of life.
D) Children probably won't master the skills essential to success in the adult world unless they begin developing those skills in the early elementary grades.