在三棱锥PABC中，G为△ABC的重心，设$\overrightarrow{PA}$=a，$\overrightarrow{PB}$=b，$\overrightarrow{PC}$=c，则$\overrightarrow{PG}$=____ （用a，b，c表示）．

增加：在缺词处加一个漏字符号（∧）并在该词下面写出该加的词

删除：把多余的词用斜线（\）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1）每处错误及其修改均仅限一词；

2）只允许修改10处，多者（从第11处起）不计分

Dear Miss Li,

    I'd like to thank you for give money to Animal Helpers. I'm sure you know that this group was set up to help disable people like me. You helped to make that possible for me to have Lucky. Lucky makes a big different to my life.

    I can't use my arms and legs well. So normally things like answering the telephone, opening and closing doors, or carrying thing are difficult for me. Then last year, to cheer me up, a friend of mine came up with a plan and helped to get me a special training dog Lucky from Animal Helpers. Lucky is clever and he can understand me when I give to him orders. I also feel lucky to have the “dog helper” because your kindness. Thank you again for changing my life.

Best wishes,

Ben Smith