Speaker A: Uh, I wonder if I could possibly use your phone.Speaker B: ______

A．Oh, I'm sorry, but it isn't working; it's out of order.

B．You are welcome. It's over there.

C．Of course. Who are you going to call

D．Yes, you can, But don't you see a public phone booth over there

在起重作业中，地锚有何作用？