皮皮学，免费搜题
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【单选题】
为了满足工作要求,活塞销的材料一般选用______并经渗碳、淬火和低温回火处理。I.低碳钢(15钢);II.中碳钢(35钢);III.合金调质钢;IV.滚动轴承钢(GCr15);V.合金渗碳钢(20Cr)。A.
Ⅰ+Ⅱ+Ⅴ
B.
Ⅰ+Ⅴ
C.
Ⅱ+Ⅴ
D.
Ⅰ+Ⅲ+Ⅴ
拍照语音搜题，微信中搜索"皮皮学"使用
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皮皮学刷刷变学霸
举一反三
【单选题】— I dropped in at your house at about ten last night, but you weren't in. — I ______ regular exercises at the club. [ ]
A.
did
B.
was doing
C.
had done
D.
have been doing
【简答题】胸腺是[填空（1）]细胞成熟的场所
【单选题】— You were out when I dropped in at your house. — Oh, I _____ for a friend from England at the airport. [ ]
A.
was waiting
B.
have waited
C.
am waiting
D.
had waited
【简答题】胸腺是 细胞分化,发育和成熟的场所。
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