传染病的基本特征是（）四个方面。
参考答案：病原体、传染性、流行病学、感染后免疫
—Do you live by yourself, Mr Wang?
—Yes. I have two sons. But ____ of them lives with me. They are now studying in America. [ ]
A. neither
B. both
C. none
D. either
He did quite well in the maths exam and he is sure he'll________between 140 and 150.[ ]
A. grade
B. score
C. mark
D. win
