1.She wasn't sure if/whether the machine was invented by Bill.
(怀疑你在这个题中多输入了一个空)
2.They were heard to sing Peking Opera in the theater last Sunday.
1.She wasn't sure if/whether the machine was invented by Bill.
(怀疑你在这个题中多输入了一个空)
2.They were heard to sing Peking Opera in the theater last Sunday.