[求助]GWD-21-1/27/34 请教!

以下我已经查过以前的确讨论,还是不明白,望指点,谢先!

GWD 21-1          D  

According to analysts, an alliance between three major personal computer companies and most of the nation’s largest local telephone companies would enable customers to receive Internet data over regular telephone lines with speeds much higher than is currently possible.

A. with speeds much higher than is

B. with speeds that are much higher than are

C. at much higher speeds as are

D. at much higher speeds than that  (E)

E. at speeds much higher than are

D的错是否为违反平行结构? at much higher speeds 与at speeds much higher 有区别否?E中的are后补全为什么?

GWD 21-27                        D

The electronics company has unveiled what it claims to be the world’s smallest network digital camcorder, the length of which is that of a handheld computer, and it weighs less than 11 ounces.

A.     to be the world’s smallest network digital camcorder, the length of which is that of a handheld computer, and it weighs

B.     to be the smallest network digital camcorder in the world, which is as long as a handheld computer, weighing

C.     is the smallest network digital camcorder in the world, which is as long as a handheld computer, and it weighs

D.     is the world’s smallest network digital camcorder, which is as long as a handheld computer and weighs  (B)

E.      is the world’s smallest network digital camcorder, the length of which is that of a handheld computer, weighing

答案为B，我选D，原因：

B的问题：

1． Claim to be一般用来连接动作的发起人和宾语，如 sb claim to be what,what和sb是同一回事；这里，it显然不能是the world’s smallest network digital camcorder, 所以不能用Claim to be，否则逻辑意义不对；

2． Which跳跃修饰不是首选；

3． Weighing在句尾，修饰对象语法上有歧义；

D的好处：

1． what it claims is the world’s smallest network digital camcorder，what是claim的宾语和is的主语，逻辑意义正确；

2． Which直接修饰camcorder，无歧义；

3． Weighs用作谓语形式，语法和逻辑意义上均准确，无歧义。

请NN指点。

GWD 21-34                C

Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments of a
dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60 million years ago,
pushing back by more than 150,000 years the earliest date when it is known that humans
made stone tools.

A. when it is known that humans made

B.   at which it is known that humans had made

C.   at which humans are known to have made

D. that humans are known to be making  (C/A)

E. of humans who were known to make

我选C，不知A和C有什么区别？

感觉上A说的是“知道人类制造石器的时间”，而C说的是“可知的人类制造石器的时间”，好象用C更符合逻辑意思。不清楚，请指点。