下列有关骨骼肌的叙述中，错误的是（　　）

依据氧化还原反应：2Ag^＋（aq）＋Cu（s）═Cu^2＋（aq）＋2Ag（s）设计的原电池如图所示。

请回答下列问题：

       One day Mrs Jones goes shopping alone(独自地). When Mr Jones comes home in the evening, she begins to tell him about a beautiful dress.  “I see it in a shop this morning,” she says, “and…” “And you want to buy it,” says Mr Jones, “how much is it?” “Fifteen pounds.” Every evening, when Mr Jones comes back from work, his wife goes on talking only about the dress. And at last, after a week, he says, “Oh, buy the dress! Here's the money!” She is very happy. But the next evening, when Mr Jones comes home and asks, “Have you got the famous(著名的) dress?” She says, “No.” Why not?” he says. “Well, it is still in the window of the shop after a week. I think nobody else wants this dress. So I think it is not a good one!”

在Rt△ABC中，∠C=90°，sinA=$\frac{4}{5}$，则cosB的值等于（  ）