Eggs are sold ____ the dozen

下列各句中，没有语病的一句是( ）

Gina’s ping-pong balls are , on the bed, on the sofa and under the chair.

Space exploration has been made _____with the development of modern science and technology. [ ]

29．—- I wonder how much you charge for your services.—- The first two are free ____ the third costs $30