He _____ football regularly for many years when he was young.
A:was playing
B:has played
C:played
D:had played
填表:
图形
长(厘米)
宽(厘米)
周长(厘米)
长方形
6
4
____
2
10
正方形
28
12
下列物质在氧气中燃烧,火星四射、生成黑色固体的是( )