I have a question about a practice test!! Why is the correct answer D? I choose A.

Question

These and other problems with the Milankovitch cycles led some researchers to seek alternative explanations for the cyclic arrival of extended ice ages. In the 1990s, it was discovered that the orbital inclination of the Earth to the sun and planets could also be responsible for climate changes. If we imagine a flat plane with the sun in the center and the planets revolving around it, the Earth slowly moves in and out of the flat plane by a few degrees, repeating the cycle every 100,000 years. Two scientists. Muller and MacDonald, have proposed that it is this orbital inclination which is ultimately responsible for the periods of glaciation and warming. They argue that because of the oscillation, the Earth periodically travels through clouds of debris, in the form of dust and meteoroids. Such debris could reduce the amount of solar energy reaching the surface of our planet. thus plunging it into regular cold periods.

 

The word "it" in the passage refers to

A, such debris

B, solar energy

C, the surface

D, our planet

Answer 1

Hi Saori;

This is the sentence...

Such debris could reduce the amount of solar energy reaching the surface of our planet. thus plunging it into regular cold periods.

Let's replace it with all available choices...

Such debris could reduce the amount of solar energy reaching the surface of our planet. thus plunging such debris into regular cold periods.

In this passage, debris does not have "cold periods".  This is not it.

Such debris could reduce the amount of solar energy reaching the surface of our planet. thus plunging solar energy into regular cold periods.

Solar energy is not otherwise discussed.  That is not it.

Such debris could reduce the amount of solar energy reaching the surface of our planet. thus plunging the surface into regular cold periods.

The word surface is only used once, and that is within this sentence.  Otherwise, such is not an issue and not likely to be it.

Such debris could reduce the amount of solar energy reaching the surface of our planet. thus plunging our planet into regular cold periods.

The paragraph discusses the cold periods our planet has experienced.  Therefore, it must be it.