A.60° B.90° C.120° D.180°
A.結(jié)構(gòu)復(fù)雜 B.堅(jiān)固耐用 C.維護(hù)方便 D.價(jià)格低廉
A.結(jié)構(gòu)簡(jiǎn)單 B.堅(jiān)固耐用 C.成本較高 D.啟動(dòng)容易