颗粒群的平均粒度表示方法有哪些?
参考答案:算术平均粒径;几何平均粒径;调和平均粒径,算术平均粒径>几何平均粒径>调和平均粒径。
艾滋病的主要传播途径有
A.性接触
B.蚊虫叮咬
C.器官移植
D.母婴垂直传播
E.输入血液及血制品
"We’re not bringing in millions of dollars," says a director of development. "But we want to make sure the demand is there before we act to the project. "()
A. of
B. off
C. on
D. for