31. To keep safe _______ an earthquake, you should remain at a spot in your room where nothing may fall on you.
There is no doubt, in my opinion,_______ matters is not the speed, but the quality of the product.
_______,but it is also a great way to lower the number of greenhouse gases in the air.
Zheng He started to sail in 1045 to “Western Seas”. In the following 28 years, he made _______ successful travels.
When _______ to our school, the new study methods are popular with all the students.
—When does our school often have a picnic? —_______,it's at the end of October.