Why does this problem exist？

What does the professor say about the invention of the elevator？

A．It created design problems for architects.

B．It was useful for transporting construction materials.

C．It enabled architects to design taller office buildings.

D．It made skyscrapers more expensive to build.

听力原文：M: Sue, I'm going to paint the roof. Will you hold the ladder for me？

W: No problem. But be careful while you're up there.

What does the man want the woman to do？

A．Hold the ladder for him.

B．Paint the roof.

C．Climb up the ladder.

D．Take care while she is up the ladder.