One of the effective ways to lessen environmental pollution is the reservation and protection of more swamps .

A．vast thick corals

B．pockets of wet land

C．warm volcanoes

D．millions of bees and wasps

缘龈炎的临床表现包括()

A．受刺激易出

B．龈缘红肿

C．软垢沉积

D．牙颈部常有牙石

E．以上均正确