A.
select xh , kch ,cj from xs_kc, kc where xs_kc.kch=kc.kch and kcm='计算机基础'
B.
select xh ,kch ,cj from xs_kc where exists ( select 1 from kc where xs_kc.kch=kc.kch and kcm='计算机基础')
C.
select xh , kch ,cj from xs_kc join kc on xs_kc.kch=kc.kch and kcm='计算机基础'
D.
select xh , kch ,cj from xs_kc where kch in (select kch from kc where kcm ='计算机基础')