Passive bilingualism is when someone comprehends more than one language but is only able to express him/herself in one of them.
a. true
b. false

This statement is A. true.
If you are bilingual, it means that you have been exposed to two languages since you were a child, and can understand both languages equally, but can express yourself in only one of them. However, you still can comprehend when somebody else is using that other language, even though you cannot reciprocate verbally.