根据句意及所给的中文或音标，写出恰当单词，使句子的意思完整、正确。

小题1:He_______(打扫)the floor yesterday．

小题2:Xi’an is one of the _______(古代的)capitals in China．

小题3:A government is a group of people who make      (决定) about the way people live．

小题4:To our great________(惊奇)，the plane has gone missing．

小题5:Some _________(公民) in Shanghai have bought this kind of robots．

依《合同法》的规定，一方以欺诈、胁迫手段或者乘人之危，使对方在违背真实意思的情况下订立的合同，属于______。

A．有效合同
B．无效合同
C．可变更、可撤销合同
D．效力待定合同