Which of the following is(are) true for a@b=b@a?
I. a@b=ab+ba
II. a@b=(a+b)(a-b)
III. a@b=(a/b)+(b/a)	Options:
A) only Ⅰ
B) only Ⅱ
C) only Ⅲ
D) only Ⅰ& Ⅲ
E) only Ⅱ & Ⅲ
If I. a@b=ab+ba, a@b=ab+ba=ba+ab=b@a (O).   If II. a@b=(a+b)(a-b), a@b=(a+b)(a-b)≠(b+a)/(b-a)=b@a (X).   If III.a@b=(a/b)+(b/a), a@b=(a/b)+(b/a)=(b/a)+(a/b)=b@a (O).   Thus, Ⅰ&amp; Ⅲ are the answers. Therefore, only Ⅰ&amp; Ⅲ is the answer.
<result>D</result>
Which of the following is(are) true for a@b=b@a?
I. a@b=ab+ba
II. a@b=(a+b)(a-b)
III. a@b=(a/b)+(b/a)