If you choose any of the three playing cards of "hearts 5, hearts 7 and hearts 9", the probability of winning "hearts 7" is () a.1b.c. 。

Test and analysis: when randomly drawing, there are three possibilities to choose one card from three different colors, and the probability of choosing "7 of hearts" is.

Comments: This question is relatively difficult, mainly to examine students' understanding of random events. Analyze and calculate the occurrence of random events in detail. ?