Father's Day has a very short history. It was started because there was a Mother's Day, and just because some Americans thought that if we had a Mother's Day, we should also have a Father's Day. Father's Day has become important in North America. And businesses found it was a good way to get people to buy a present for their father from their shops.
By the way, very few countries have a Father's Day, though some have a Children's Day, or a special day for boys and another for girls. More and more countries are having Mother's Day, so maybe Father's Day will also become popular before too long. Now, what do people in North America do on Father's Day? The newspapers, radios, and TV tell children what they should do — buy, buy, buy, buy, buy a Father's Day present for your father. They even tell a wife to buy, buy, buy, and buy a Father's Day present — not for her father but for her husband, even if he is not yet a father. And they tell grandchildren to buy, buy, buy, and buy a Father's Day present for their grandfathers.
The important thing to remember about Father's Day is that American children can show their love to their fathers in a more open way.

分式$\frac{x-2}{{\left(x-1\right)}^2}$、$\frac{2x-3}{{\left(x-1\right)}^{3^{}}}$、$\frac{5}{x-1}$的最简公分母是（　　）

a．如图甲，将毛巾铺在水平木板上，让小车从斜面顶端由静止滑下，观察小车在水平面上通过的距离．

b．如图乙，取下毛巾，将棉布铺在斜面和木板上，让小车从斜面顶端由静止滑下，观察小车在水平面上通过的距离．

c．如图丙，取下棉布，让小车从斜面顶端由静止滑下，观察小车在水平面上通过的距离．

请针对以上操作回答下列问题：

“冬虫夏草”，通称虫草．冬天在感染的昆虫体内形成菌核，次年夏季温暖潮湿，适于菌体生长时，似棵野草，故名“冬虫夏草”．据此可知“冬虫夏草”是（  ）