若|a|=8，|b|=6。

（1）求a+b的值；

（2）若|a+b|=a+b，求b-a的值；

（3）若|a-b|=b-a，求a+b的值。

Mary forgot（）a letter to her mother, so she wrote to her just now.

A.writing

B.to write

C.having wrote

D.to have written