求救!!!在线等回复,急!!先谢了

songnaUID: 2151333

21.The Pacific Ocean (comprises)   almost the   entire   boundary western of North and South America.
24.Because of their  rapidly changing (economically) fortunes, many frontier towns of the American West underwent spectacular fluctuations in population in the nineteenth century.

30.Since prehistoric times ,artists (have been) arranged colors on surfaces (in ways)    (that express) their ideas (about people) ,the world ,and religion.

37.The element potassium makes up    less than one half( percentage )of the human body.

这四道改错题不懂,(括号中的词是错的)(还有第二中的rapidly为什么没错?changing 不该形容词修饰吗???)
高手来给讲讲!!!
万分感谢!

songnaUID: 2151333

30.Since prehistoric times ,artists (have been) arranged colors on surfaces in ways that  express their ideas  about people  ,the world ,and religion.
只有(have been)错了!

nannanyoyoUID: 2128943

21. comprises应该没错，后面boundary western 应改为western boundary
22. economically 应改为形容词来修饰名词 fortunes。rapidly（副词）修饰分词短语
changing economical fortunes
30.去掉been 。这里是主动语态
34.改为percent。

wingerweskerUID: 2154168

21 不知道
24 changing这里动名词形式作形容词修饰fortunes，故economically应用形容词economical
30 artists作主语，have been为被动语态
37 percentage专指百分比，百分率

翦瞳UID: 184872

percentage:
for example:
0.98 equals a percentage of 98.
a small percentage of the audience
The percentage of unskilled workers is small.
percent:
The report states that 42 percent of the alumni contributed to the endowment.
总结：可能表达百分多少，用percent，percentage指的就是那个比值，呵呵，其实我也不是太懂

20051222UID: 2169624

1/2用one half就够了
percentage表示百分比，在这里是多余的