“苦苦思索而弄清楚”可以用以下几种英语表达：
1、 Ponder deeply and finally figure it out
“ponder deeply”表示“苦苦思索”，“figure it out”表示“弄清楚”。
2、 Struggle to think through and finally understand
“struggle to think through”体现了苦苦思索的过程，“finally understand”表示最终弄清楚。
3、 Ruminate over and come to a clear understanding
“ruminate over”有反复思考、苦思冥想的意思，“come to a clear understanding”表示最终弄清楚、达到清晰的理解。
4、 Delve into deep thought and eventually clarify
“delve into deep thought”表示深入思考、苦苦思索，“eventually clarify”表示最终弄清楚、澄清。
这些表达都体现了“苦苦思索而弄清楚”的含义，可以根据具体语境和表达习惯选择合适的短语。