设<img src="https://static.zxtiku.com/wangke/imgs/topic/76b644910898e1be015c98defdfab3b5.jpg"/>个电子管的寿命<img src="https://static.zxtiku.com/wangke/imgs/topic/e1ffb634abf7d091a47a5375156f0a0f.jpg"/>(<img src="https://static.zxtiku.com/wangke/imgs/topic/db26ebf982be880f45bb0aa67166594f.jpg"/>)独立同分布，且<img src="https://static.zxtiku.com/wangke/imgs/topic/3fdd4bd9ee4ab0633f5e390f88c22cdf.jpg"/>(<img src="https://static.zxtiku.com/wangke/imgs/topic/030e044b318cfe7c7c420610edec82ba.jpg"/>)，则<img src="https://static.zxtiku.com/wangke/imgs/topic/b4d60e2671e6b1ffae86660efa6e24ad.jpg"/>个电子管的平均寿命<img src="https://static.zxtiku.com/wangke/imgs/topic/99784d3cdc6da8e4eddc908134982aa1.jpg"/>的方差<img src="https://static.zxtiku.com/wangke/imgs/topic/dbae7384153c450107e92d44a4823e6f.jpg"/>（）． A. A B. 0.1A C. 0.2A D. 10A