求教一道数学排列组合的题,说九个字母POSSESSES被写在9张不同的卡片上,然后从中随机抽出四张卡片.（1）问一共能抽

求教一道数学排列组合的题,
说九个字母POSSESSES被写在9张不同的卡片上,然后从中随机抽出四张卡片.
（1）问一共能抽出多少组不同的四张卡片.（组合）
（2）一共有多少种可能出现的四张卡片的排列.（排列）
可能说的不是很清楚,是一道英文题,原文如下.
The letters of the word POSSESSES are written on nine cards,one on each card.The cards are shuffled and four of them are selected and arranged in a straight line.
(a)How many possible selections are there of four letters?
(b)How many arrangements are there of four letters?
奖励你五十分,前提条件是过程要清楚,要能让我看明白.