For most of their history,especially since the 1860's,New York City has been undergoing major ethnic population changes.(their)改为its,因为New York City为单数.
Most of our ideas of what ancientpeople looked and dressed come from the works of Renaissance artists.(what)改为how,look不能用what修饰,how可以修饰动作.
All nations may have to make fundamental changes in their economic,political and the technological institutions if they are to preserve the environment.(the technological institutions)
改为technological institutions,the作为多余的冠词与their冲突.
Mass achusettes was first explored in the late sixteenth and early seventeenth centuries,and the first permanent settlement at Ply mouth in 1620.(settlement)改为settled,settlement为名词不合结构
Sarah Vaughan had a voice like a perfect instrument,and it was an instrument that she knew how to use it with the utmost skill.(to use it)删去it,it同时作为主语宾语赘余.