Scientists classify rocks a. by composition and texture. c. by mass. b. by volume. d. by color and size.

 i think it would be a. I know this is a late answer but i need points. 
 

hope this helps anyways.

Answer;

A. by composition and texture.

Explanation;The composition of rocks is among the key characteristics that are used to classify rocks as it determines and reflects how a certain rock was formed. This determines whether a rock is sedimentary, metamorphic or igneous. For instance a rock with strong banding and orientation of minerals is classified as metamorphic rock.The texture on the other hand is another factor that determines the classification of rocks. Textures reveals the size shapes of mineral grains and also other constituents of a rock, and also the relationship between the shapes and sizes of a rock.

The answer is a) taiga because taigas are cold

Ireally don’t know