25.   The physical structure of the human eye enables it to sense light of wavelengths up to 0.0005 millimeters; infrared radiation, however, is invisible because its wavelength—0.1 millimeters—is too long to be registered by the eye.

(A) infrared radiation, however, is invisible because its wavelength—0.1 millimeters—is too long to be registered by the eye

(B) however, the wavelength of infrared radiation—0.1 millimeters—is too long to be registered by the eye making it invisible

(C) infrared radiation, however, is invisible because its wavelength—0.1 millimeters—is too long for the eye to register it

(D) however, because the wavelength of infrared radiation is 0.1 millimeters, it is too long for the eye to register and thus invisible

(E) however, infrared radiation has a wavelength of 0.1 millimeters that is too long for the eye to register, thus making it invisible

答案是A, 可是C 选项为什么不对呢？

C: "it" does not have a clear referent, "it" can refers to "infrared radiation", or "its wavelength".

此题考察代词指代。