50. To keep your classroom clean, please 　　　　　　waste paper whenever you see it.

49. You can wave your hands to them instead of 　　　　　　with them.

48. You shouldn’t beat him, but tell him why -　　　　　 　, he is a child.

47. It’s impolite to 　　　　　　friends’ homes without calling first in Switzerland.

46. The driver 　　　　　　to offer me a lift.

45. Please don’t 　　　　　　. The students are taking an exam.

44. Bill 　　　　　　reading newspapers over breakfast.

43. This machine can 　　　　　　the vegetables.

42. A journey always 　　　　　　the first step.

41. My uncle 　　　　　　Chinese 　　　　　　.