题目

用所给词的正确形式填空。 1.How many___________(firefighters, firefighter) are there? 2. My mother is a _______(writer/write).3. What_________(do/does) your cousin do?___________(His/He's) a cook. 4. My father is a ________(doctor, teacher). He has a lot of students. 5. She’s my aunt. She’s a __________________(office worker, nurse). 答案：【答案】1. firefighters 2. writer 3. does He’s 4. teacher 5. nurse 【解析】略已知四棱柱ABCD﹣A1B1C1D1的底面是边长为2的菱形，且∠BAD= ，AA1⊥平面ABCD，AA1=1，设E为CD中点 （1）求证：D1E⊥平面BEC1（2）点F在线段A1B1上，且AF∥平面BEC1 ， 求平面ADF和平面BEC1所成锐角的余弦值．