由向量的数量积得坐标表示可得，a•b=-1×2+4×(-1)=-6
故选：D
根据句意及首字母提示补全单词。
1. The p_____ of this passage is to talk about a program that helps homeless people.
2. A_____ Jim's uncle is old, he looks very strong and healthy.
3. I have made p_____ for the coming test.
4. There will be an important c_____ in the meeting room this afternoon.
5. The students are doing physics e_____ in the lab.
一外伤致脾破裂的病人，血压10.7/8kPa(80/ 60mmHg)，脉搏130次/分。估计失血量在
A．400～600ml
B．600～800ml
C．800～1600ml
D．1600～2000ml
