singular or plural: ride a bike

[dido4]

There are two people in a picture. Each is riding a bike. There are two bikes, and they are riding their own bikes.

The question is:
Can they ride a bike?
The answer is:
Yes, they can ride a bike.

Q1:Isn't it:
They can ride bikes.
Why is "ride a bike"? There are two people there. Don't know why. The answer is singular not plural. Why?

[bhaisahab]

Originally Posted by dido4

There are two people in a picture. Each is riding a bike. There are two bikes, and they are riding their own bikes.

The question is:
Can they ride a bike?
The answer is:
Yes, they can ride a bike.

Q1:Isn't it:
They can ride bikes.
Why is "ride a bike"? There are two people there. Don't know why. The answer is singular not plural. Why?

It's a strange question, if the picture shows people riding bikes, then it is obvious they know how to do it. I imagine that this is a lesson about 'can', the ability to do something. If the question is 'Can (do they know how to) ride a bike?' Then the best response is 'Yes they can.'

[David L.]

"they can ride bikes' means that each and everyone of them can ride bikes!
How dexterous of them. Most people can only ride one bike at a time.

The picture is showing that, give them a bike, any bike, they can ride it. Yes, they are showing that they know how to ride a bike.