线粒体是生物细胞中提供能量的“动力车间”，是一种半自主细胞器。下面有关线粒体的叙述正确的是 （  ）

若N_A代表阿伏加德罗常数的值，下列说法中正确的是

你班进行“背起行囊走四方”的综合性学习活动，请你完成下面的任务。

活动一：走进大自然。

阅读理解
A
    My name's Li Yan．I'm from Belling and I'm 13 years old.I study in No．1 Middle School．I'm in Class 2．Grade 7．I'm in the school music club．I can play the guitar well and I am good at playing the piano．Lang Lang is my favorite musician．I dream of being a musician like him．
    LiYue is my sister．We are twins(双胞胎)．We go to the same school， but she is in Class 4．Grade 7．She can play ping-pong very well and she is in the sports club．She likes Zhang Jike and Ma Long best．She often watches them play ping-pong on TV.
    My sister and I are learning how to swim．We are not good at it now,but we are trying our best(尽我们最大的努力)to learn it．It is a really healthy sport．
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如图所示．abed为质量M=3.0Kg的“ ”型导轨（电阻不计），放在光滑绝缘的、倾角为θ=53^°的斜面上，绝缘光滑的立柱e，、f垂直于斜面固定，质童m=2.0Kg的金属棒PQ平行于ad边压在导轨和立柱．、f上．导轨和金属捧都处于匀强磁场中，磁场以OO′为界，OO′左侧的磁场方向垂直于斜面向上，右侧的磁场方向沿斜面向下，磁感应强度大小都为B=1.0T．导轨的ad段长L=1.0m，棒PQ单位长度的电阻为r₀=0.5Ω/m，金属棒PQ与“ ”型导轨始终接触良好且两者间的摩擦力是两者间正压力的μ=0.25倍．设导轨和斜面都足够长，将导轨无初速释放，（取g=10m/s²，sin53°=0.8，cos53°=0.6图中的MN、ad、OO′、PQ彼此平行且处在水平方向） 求：