36套阅读 exercise 12 关于蝙蝠的阅读

fadotianUID: 2733387

就列出这篇阅读的第二段。
The FM signals report information about target characteristics that modify the timing and the fine frequency structure, or spectrum, of echoes—for example, the target‘s size, shape, texture, surface structure, and direction in space. Because of their narrow 15 bandwidth, CF signals portray only the target‘s presence and, in the case of some bat species, its motion relative to the bat‘s. Responding to changes in the CF echo‘s frequency, bats of some species correct in flight for the direction and velocity of their moving prey.

According to the passage, the information provided to the bat by CF echoes differs from that provided
by FM echoes in which of the following ways?
(A) Only CF echoes alert the bat to moving targets.
(B) Only CF echoes identify the range of widely spaced targets.
(C) Only CF echoes report the target‘s presence to the bat.
(D) In some species, CF echoes enable the bat to judge whether it is closing in on its target.
(E) In some species, CF echoes enable the bat to discriminate the size of its target and the
direction in which the target is moving.
为什么选D?
明明C对应于文中的第3行：CF signal portray only the target's presence.......

zcycloneUID: 3184589

楼主，原文的意思是“CF只能描绘出。。。”而不是“只有CF能描绘出。。。”
原文中FM也能描绘出target‘s size, shape, texture, surface structure，这些都是presence
这是我的理解，希望对你有帮助

MadaooUID: 2870014

CF only/ only CF 的区别吧