The thief who was caught stealing on the bus couldn't ______ the fact that the passenger's purse was found in his pocket.
A：answer for
B：leave for
C：account for
D：care for
工业上制造镁粉是将镁蒸气在气体中冷却．可作为冷却气体的是（ ）
①空气 ②CO2 ③Ar ④H2 ⑤N2．
用加减法解方程组x+y=5x-y=-1C中，消x用____法，消y用____法（ ）
