It would be the textbook glossary. A dictionary would be equally useful, but in a science class the teacher would want students to rely on the textbook glossary.
The word "either" is a correlative. The answer is D. This is because a correlative conjunction connects two nouns and ideas that relates to each other. Either uses "or" so it connects two choices in one situation.
Read the lines from Act I, scene v of Romeo and Juliet.
Jim said he reckoned the widow was partly right and pap was partly right; so the best way would be for us to pick out two or three things from the list and say we wouldn't borrow them any more—then he reckoned it wouldn't be no harm to borrow the others. ion: