单句语法填空
1. Have you ever asked yourself why people often have trouble __________（learn）English？
2. This got me __________（think）why English can be a crazy language __________（learn）．
3. __________（speak）of home，why aren’t homework and housework the same thing？
4. When you see the capitalized “WHO” in a medical report，do you read it __________ the “who” in “Who’s that？”
5. That is __________ when the stars are out，they are visible，__________ when the lights are out，they are invisible．