题目

When your parents advise you to “get an education” in order to raise your income, they tell you only half the truth. What they really mean is to get just enough education to provide manpower（人力资源） for your society, but not so much that you prove an embarrassment to your society. Get a high school diploma, at least. Without that, you will be occupationally dead unless your name happens to be George Bernard Shaw or Thomas Alva Edison, and you can successfully dropout in grade school. Get a college degree, if possible. With a B. A., you are on the launching pad. But now you4．如图，三棱柱ABC-A1B1C1中，CA=CB，AB=AA1，∠BAA1=60°．（Ⅰ）证明：AB⊥A1C；（Ⅱ）若平面ABC⊥平面AA1B1B，AB=CB，求直线A1C与平面BB1C1C所成角的正弦值．