【正确答案】：
（1）CHANGE IN SOUND AND SPELLING. SOME HOMONYMS ARE NATIVE BY ORIGIN, DERIVED FROM DIFFERENT EARLIER FORMS IN OLD ENGLISH. THE CHANGE IN SOUND AND SPELLING GRADUALLY MADE THEM IDENTICAL IN MODERN ENGLISH, E. G. LONG ADJ. NOT SHORT, FROM LANG(OE); LONG V. TO WANT VERY MUCH, FROM LANGIAN(OE).
（2）BORROWING. MANY WORDS OF FOREIGN ORIGIN COINCIDE IN SOUND AND/OR SPELLING WITH THOSE OF NATIVE ORIGIN OR WITH THOSE OF OTHER FOREIGN ORIGIN, E. G. BALL N. A ROUND OBJECT TO PLAY WITH, FROM BEALLU (OE); BALL N. A DANCING PARTY, BORROWED FROM BALLER(OF).
（3）SHORTENING. MANY SHORTENED FORMS OF WORDS HAPPEN TO BE IDENTICAL WITH OTHER WORDS IN SPELLING OR SOUND, E. G. AD N. SHORTENED FROM ADVERTISEMENT; ADD V. TO CAUSE AN INCREASE. 
【题目解析】：（1）语音和拼写变化。有些同形同音异义词来源于本族词语，派生自古英语中的不同早期形式。语音和拼写方面的变化使得它们在现代英语中逐渐变得相同起来，如：long（长的） adj. 源自lang(OE 古英语)，long v. 渴求，源自 langian(OE 古英语).（2）借用。许多外来词在发音和/或拼写上与本国词或其他外来词一致，如：ball n. 球, 源自 beallu (OE); ball n. 舞会, 源自 baller(OF).（3）缩略法。很多缩略词的形式正好与其他词的拼写或语音雷同，如：ad n. （广告）的缩略形式; add v. 增加，增添.