Itisusefultoscience_______theearthasanobjectinspace.
It________asashocktorealizethatIwasnotaloneintheroom.
WhenIcamethroughthecustomsattheairport,Ihadtopay________onaclockIhadbought.
Heaskedmewhethermybrother________(fly)toBeijing.
用和平赎买的方法对_________进行改造。
