当a=4,b=0.5时,0.9a-0.2b=[ ]
A.2.6
B.3.5
C.2.5
答案:B
词汇。
1.My ________ (钥匙) are on the table.
2.—________ (在哪里)is the baseball?
—I don't know.
3. My backpack is ________ (在……下面) the dresser.
4. Please ________ (带来) your dictionary to school tomorrow.
5. The boy is ________ (在两者之间) Betty and Kate.
一束光线垂直入射到平面镜上,反射角为______;若一束光线的反射光线与界面成30°,则反射光线与入射光线的夹角为______。