引起铸件热裂的原因较多，指出下列项次中，会引起热裂的条目（）
A.线收缩受阻
B.厚薄悬殊
C.落砂过早
D.硫磷偏低
参考答案：A, B, C
Dear me! Just _________ at the time! I _________ no idea it was so late.
A．look, have
B．looking, had
C．look, had
D．looking, have
“三无”是指无______、无______、无______。
