551.Once positioned in space, the Hubble Space Telescope will capture light from sources twenty times fainter compared to those that can be detected by ground-based instruments. (A) compared to those that can be detected (B) compared to those they can detect (C) than that can be detected (D) than those that can be detected (E) than those detecting
551.Once positioned in space, the Hubble Space Telescope will capture light from sources twenty times fainter(表明需要比较级than) (D) than those(代sources) that can be detected by ground-based instruments(表明前边需被动形式).