Would you please keep silent．'? The weather report_______and I want to listen．

Great sums of money have been spent, for example in the...

单项选择题Great sums of money have been spent, for example in the deserts of Egypt, in __________ oil. Sometimes little is found. When we buy a few gallons of petrol for our cars, we pay not only the cost of the petrol, but also part of the cost of the search that is always going on.

When we reached the station the train had not arrived y...

单项选择题When we reached the station the train had not arrived yet；so we_______．

太阳系的行星绕太阳运动时，其机械能守恒，动量矩不守恒。（ ）

单项选择题太阳系的行星绕太阳运动时，其机械能守恒，动量矩不守恒。（ ）