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Annie has four cards of different colors. She writes letter $B$ on the red card and blue card, and writes letter $O$ on the yellow card and green card. Now Annie puts the four cards in a box. Bob is going to draw three of them from the box randomly. How many different possible results can Bob get? Among them, how many can Bob get his name? 
Overseas Competition->Knowledge Point->Counting Modules->Questions Involving Enumeration->Enumeration
There are $4$ ways to choose three from four. Two $B$s with one $O$ can form Bob\textquotesingle s name. Thus, $2$ of the $4$ ways can get Bob\textquotesingle s name. 