煤中灰分与发热量之间具有()
A.正相关性;
B.负相关性;
C.无相关性
参考答案:B
(2010·全国卷Ⅱ)The doctor thought ________ would be good for you to have a holiday.
A.this
B.that
C.one
D.it
Access 2000数据库文件使用()作为扩展名。
A.MDB
B.ACC
C.DBF
D.DB