1. According to recent research, the critical period for developing language skills is between the ages of three and five and a half years.
A. The read-to child already has a large vocabulary and a sense of grammar and sentence structure.
B. Children who are read to in these years have a far better chance of reading well in school, indeed, of doing well in all subject.
C. And the reason is actually quiet simple.
D. This correlation is far and away the highest yet found between home influences and school success.
6. His comprehension of language is therefore very high.
(1) and (B) is a mandatory pair because of presence of the pronoun "these" in statement B. Only answer option D fulfills this criteria. Hence answer option "D".