Guessing the words you are comparing are "plain" and "plains" the correct answer is C. Homophone; the two words are pronounced the same but have different meanings and sometimes different spellings. Because plain and plains are words that sound alike; but they have different meanings as in "plain cream cheese" the word plain means to be pure while the word plains in the part "crossing the plains in Kansas" is referring to the extensive area of Kansas country; lastly they have slightly different spellings as plain and plains.
Option A. Homograph is wrong because the correct definition is two words are written the same, not pronounced the same.
Option B. Homophone is wrong because the correct definition is two words are pronounced the same, not written the same.
Option D. Homograph is wrong because in this case they are written the same as the bear (the verb to carry) and the bear (the animal). But for plain and plains they are not identical as one has a S.