【答案】
分析:根据比例的基本性质:两内项之积等于两外项之积即可解答.
解答:解:A、
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103201736020582879/SYS201311032017360205828015_DA/0.png)
=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103201736020582879/SYS201311032017360205828015_DA/1.png)
的两个外项是m、n,两个内项是a、b,所以ab=mn,正确,故本选项不符合题意;
B、
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103201736020582879/SYS201311032017360205828015_DA/2.png)
=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103201736020582879/SYS201311032017360205828015_DA/3.png)
的两个内项是n、m,两个外项是a、b,所以ab=mn,正确,故本选项不符合题意;
C、
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103201736020582879/SYS201311032017360205828015_DA/4.png)
=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103201736020582879/SYS201311032017360205828015_DA/5.png)
的两个内项是a、n,两个外项是m、b,所以an=bm,错误,故本选项符合题意;
D、
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103201736020582879/SYS201311032017360205828015_DA/6.png)
=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131103201736020582879/SYS201311032017360205828015_DA/7.png)
的两个外项是a、b,两个内项是n、m,所以ab=mn,正确,故本选项不符合题意.
故选C.
点评:本题是基础题,考查了比例的基本性质,比较简单.