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.