一个电压为U0的直流恒压源,通过开关K与电感L和电阻R串联构成闭合回路。现以开关闭合时开始计时,通过电感的电流为( )。<br>·<img src="/lqwvjeImg/ae/aead0d1f28c257be7afdb3b4f4eec79c.png"style="width:86px;height:45px;"><br>·<img src="/lqwvjeImg/04/04cbab5fe7c389f71ca26ae694b45ef6.png"style="width:86px;height:45px;"><br>·<img src="/lqwvjeImg/ae/aee66f60423a067ef1e68594af0b9d17.png"style="width:81px;height:45px;"><br>· <img src="/lqwvjeImg/15/15bbdadc46aa2d81a9d8eaeac6c65af0.png"style="width:92px;height:45px;">