What are the three major sources of homonyms?Match with the foll

What are the three major sources of homonyms?Match with the following example words: rock, ball, ear.
【正确答案】：

CHANGE IN SOUND AND SPELLING-EAR.
BORROWING-BALL.
SHORTENING-ROCK. 

【题目解析】：声音和拼写的变化。 borrowing-ball。 shortening-rock。