听力原文：Authorities in Nepal say Maoist rebels have killed at least twenty-one policemen

听力原文： Authorities in Nepal say Maoist rebels have killed at least twenty-one policemen and wounded sixteen others in an ambush in the western part of the country. A police official says the attack took place at a village, four hundred and fifty kilometers west of Katmandu. He says the rebels planted a landmine that exploded as the trucks passed. Maoists began the armed campaign in 1996 to replace Nepal's constitutional monarchy with a socialist state.

The policemen were killed and wounded______.

A．in a grenade attack

B．in a rocket attack

C．in a landmine explosion

D．in a suicide bombing