The underlined word "event" in the first paragraph refers to______.

A．A human being.
B．A spider.
C．A truck.
D．A drill.

A．to tell people how serious the damage caused by landslides is
B．to tell people that sending workers to stabilize mountainsides is a risky job
C．to introduce a product that can be used to stabilize mountainsides
D．to show people how to use a new robot