Tom and Lily have arrived, but（）students of the class are not here yet.

A．to be more successful in his career
B．to be more specialized in his field
C．to solve technical problems
D．to develop his professional skill

A．researchers explain the meaning of a gesture according to the situation in which it is used
B．researchers believe that one gesture has only one meaning
C．researchers think that one certain gesture can not be used in another situation
D．researchers look for patterns in textbooks to explain the meaning of a gesture