15+20=____ 5×4=____  31+13=____  9×9=____ 3×4+7=____

42-12=____  6+3=____  7×8=____  23-7=____  6×4-6=____

— Mum, I don't quite understand the Chinese saying.

— Dear, don't worry. _______ the years go by, you will get to know it.

Mary's grandpa is always ______ in the mountain village. He tells her he feels very______. So she's going to visit him next week.

酒后驾车是引发交通事故的重要原因。交警对驾驶员进行呼气酒精检测的原理是：橙色的K₂Cr₂O₇酸性水溶液遇乙醇迅速生成蓝绿色Cr³⁺。下列对乙醇的描述与此测定原理有关的是（）
①乙醇沸点低   ②乙醇密度比水小  ③乙醇有还原性   ④乙醇是烃的含氧化合物

下列计算正确的是（　　）