一袋中有7个大小相同的小球，其中有2个红球，3个黄球，2个蓝球，从中任取3个小球．

（I）求红、黄、蓝三种颜色的小球各取1个的概率；

（II）设X表示取到的蓝色小球的个数，求X的分布列和数学期望．

根据短文理解，选择正确答案。

    Tea to the Chinese is like coffee to the Americans. It's something that they can't live without.

    Chinese tea has a history of more than 5,000 years. It was most popular during the Tang Dynasty. China has many kinds of tea. White, yellow, green, oolong (乌龙茶), black and dark tea are the six main kinds.

    People in different places drink tea in their own way. People in Guangdong and Fujian love to drink “Kung Fu Tea” in small tea cups. They clean the teapot (茶壶) first with boiling water to warm it up. Then they fill the teapot with tea leaves before putting in the boiling water.

    In Beijing, people love jasmine flower（茉莉花）green tea. In Tibet, butter tea (酥油茶) is a popular drink to build up energy.

    There are rules to follow when we serve tea to others. Most importantly, remember to make the cup only seven-tenths full. If the cup is too full, it makes the cup too hot for them to hold.

根据意思写出词语。

①表示出乎意料，竟然。____

②无益地耗费力气。____

③随随便便，不放在心上。____

一个盛水的平底茶杯，总质量为450g，底面积为50cm²，放在面积为1m²的水平桌面上，杯子和水所受的重力为____N，杯子对桌面的压强为____Pa。