下列说法正确的一项是（   ）。

    Jack1in a small town in England.He always stayed in England2 his holidays, but last year he thought, “I've never been to3countries. All my friends have been to Spain，4they like it very much, so this year I'm going there, too.” So he got on a5to Spain and6at the airport of the capital, Madrid, and stayed in a hotel for a few days. On the first morning he went7for a walk. In England people drive on the left, but in Spain they drive on the right. Jack forgot about this, so8he was walking on a busy street, a bicycle knocked him down.

    Jack 9on the ground for a few minutes and then he sat up and said, “Where am I？”

    Just then an old man selling maps went past him. When he heard Jack's words, he said to him10, “Maps of the city, sir？”

一名学生军训时连续射靶6次，命中的环数分别为6，8，5，6，9，8．则这名学生射击环数的方差是____．