第二段具体解释的是上文提到关于use two variables to evaluate suppliers的strategy. 是这种strategy会导致四种结果. D选项逻辑错误，这四种结果是由strategy导致的，而不是problem( shelter suppliers from rigorous......)导致的
B，Unlike many United States cities, where a river is no longer the focal point of urban life, the river in San Antonio winds through the middle of the business district.而后面is the city's most popular attraction的主语已经变成了the River Walk, or Paseo del Rio,不再是the river的性质。不再是市中心和穿过商业中心这两个性质unlike不起来，B错误！
E，倒装
No longer do many cities in the United States have a river as the focal point of urban life,
=Many cities in the United States no longer have a river as the focal point of urban life,
1、from……to……表达了先后顺序，then to多余，B错！
2、move可以及物也可以不及物，I move the desk to a corner.
当表示移动自己时，不用说move oneself，我搬去了非洲，I move to Africa.不能说I move myself to Africa.
1、regard A as B或regard A as adj，as相当于be
regard manner as efficient
2、the early hominids' manner is less efficient than that of modern human beings
B中，it 是同物指代，自己不能跟自己比，错！
1、present as little risk as one chance in a million 和present a risk as little as one chance in a million都是正确的表达方式
2、a risk of sth/doing……的风险，a risk to sb/sth对……是个风险，a risk that……，风险的内容是……，没有a risk for doing和a risk to do
E，it只能指代单数名词risk，present a risk for the risk to cause cancer，错！
A because of B 表示B led to A, 可以理解为先发生了b，之后发生了a，这两件事是独立的，是不同的事情
可以说：more littering has occurred because of the lax enforcement of laws against littering.
不能说： more littering has occurred because people have been throwing bottles along the side of the road。人们在路边扔瓶子和垃圾越来越多是一件事情。
D，
这里有越来越多的轨道附近的垃圾和这些国际废弃物，比如……也是一件事情，不能用because of修饰
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还是不是很理解B里面的argument accept是什么意思