What’s the reason for twins to be at a disadvantage in their intellectual development?

• A、They can only understand their own private language

• B、They communicate with outsiders less than non-twins.

• C、There is little stimulation for them.

• D、Adults don’t like to talk with them.

29（）

• A、putting up

• B、making up

• C、setting up

• D、looking up

59（）