Many Theorists Believe That Important Aspects of the Acquisition of Grammar

Many theorists believe that important aspects of the acquisition of grammar are biologically predetermined.To determine what knowledge is innate,what type of cross-linguistic studies have been done?

A) Those that assess how quickly children enter the naming explosion phase.
B) Those that assess if children are referential or expressive in their language usage.
C) Those that assess what is hard and what is easy for children to acquire.
D) Those that assess the match between adults' and children's styles across many languages.