层度接近于零的砂浆（）。
A.易离析；
B.施工操作困难；
C.易产生干缩裂缝；
D.宜加入微沬剂。
参考答案：C
句型转换。
1. I know. (改成否定句)
I __________ know.
2. Christmas is December twenty-fifth. (对画线部分提问)
__________ is Christams?
3. Jack runs as quickly as Jim. (改为否定句)
Jack __________ __________ __________ quickly as Jim.
4. His sweater is yellow. (对画线部分提问)
__________ __________is his sweater?
5. My name is Li Ming. (对画线部分提问)
__________ is your name?
北京2008年奥运会火炬接力传递活动在南京传递的路线全程约12900m，将12900m用科学记数表示为______m．
