随机变量X在下面区间上取值,使函数<imgwidth="80"height="21"v:shapes="_x0000_i1167"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image234.png">成为它的概率密度的是()
①
<imgwidth="46"height="46"v:shapes="_x0000_i1168"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image236.png">
②
<imgwidth="49"height="46"v:shapes="_x0000_i1169"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image238.png">
③
<imgwidth="39"height="27"v:shapes="_x0000_i1170"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image240.png">
④
<imgwidth="70"height="46"v:shapes="_x0000_i1171"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image242.png">