设总体X的密度函数为<img src=https://huaweicloudobs.ahjxjy.cn/E6E7D32F09385C824CE9543D307913D6.png style=vertical-align: middle;/>则θ的极大似然估计量为( )
①
<img src=https://huaweicloudobs.ahjxjy.cn/F6E90CCE87B4440AA1D46F4864A3CE90.png style=vertical-align: middle;/>
②
<img src=https://huaweicloudobs.ahjxjy.cn/0E541A7790339DD7EDC0E6CC498FBA9B.png style=vertical-align: middle;/>
③
<img src=https://huaweicloudobs.ahjxjy.cn/28DDDC54A52871B5E2C163823082B1B0.png style=vertical-align: middle;/>
④
<img src=https://huaweicloudobs.ahjxjy.cn/B56C8BDBA4888D39FB11BCD0DCFA9FD1.png style=vertical-align: middle;/>