企业可选择的新产品开发方式主要有（）
A.自行研制开发
B.模拟开发
C.引进开发
D.组合开发
E.合作开发
参考答案：A, C, E
Every possible means _______to prevent the air pollution, but the sky is still not clear.
A．are being used
B．have been used
C．has been used
D．had been used
设复数z满足|z|＝|z－1|＝1，则复数z的实部为________．
