21.A. should B. will

　　C. can D. must

　　22.A. concerned about B. interested in

　　C. happy with D. afraid of

　　23.A. lose heart B. get excited

　　C. gain confidence D. stay calm

　　24.A. faced B. brought

　　C. exposed D. connected

　　25.A. In reality B. In nature

　　C. On the contrary D. On one hand

　　26.A. in B. during

　　C. among D. on

　　27.A. unusually B. unlikely

　　C. ordinarily D. normally

　　28.A. in B. under

　　C. by D. about

　　29.A. dangerous B. risky

　　C. unsafe D. endangered

　　30.A. established B. blocked

　　C. offered D. destroyed