In Savage-Rumbaugh Et Al

In Savage-Rumbaugh et al.'s study what is the probable reason for Kanzi's faster rate of word acquisition compared with Mulika?

A) Mulika preferred gestures
B) Kanzi was older than Mulika
C) Kanzi is a pygmy chimp, while Mulika is a common chimp
D) Kanzi had probably acquired some words from watching his mother
E) Mulika did not like using the lexigram