Word显示未安装感叹号的托盘

In my project, I'm trying to reach trays of the installed printers and successfully doing it. If some paper sources of the selected printer are not installed I don't show them in the paper source combo. In the mean time, Word also don't show them in the print dialog - paper/quality tab. But when Word shows non-installed trays with an exclamation mark, my combo also shows them (without any mark of course). Why does Word show them and what is the meaning of that exclamation mark? And how can I avoid those trays?In my project, I'm trying to reach trays of the