how to deal with 5years old who doesn't want to answer your questions?

Hi, my son (5 years old now). He like to talk! Very talkative sometime. But he will keep quite or silence when you asking him a question. What I means is when I ask a very formal question like do you understand what does recycle means? ( My situation is he understands the meaning but he just doesn't want to speak it out) How to encourage him to answer even the answer might be wrong... I wish he could try to speak out rather than just keep silent... Do you have any advice??