听下面一段较长对话，回答以下小题。
【小题1】What are the speakers mainly talking about?

A．A certain ball made in space.

B．A research plan made in space.

C．A problem in making things in space.

【小题2】What might the balls most probably be used for?

A．Children’s games.

B．Medical research.

C．Earth protection.

【小题3】Why have astronauts made the ball in space?

A．To keep them smaller.

B．To keep them perfectly round.

C．To produce them more cheaply.