难办用英语怎么说？

难办

例句

• This is one of the most puzzling cases I have ever run up against. 这是我经手的最难办的案件之一.
• Imposing speed restrictions is easy, but forcing motorists to observe them is trickier. 限制车速容易，但强制司机遵守这些限速规定就难办多了。
• The impurity of supposedly pure subcellular fractions is a constant threat to the plant biochemist. 以为亚细胞组分很纯而实际不纯的情况,一直是植物化学家感到难办的问题.
• Imposing speed restrictions is easy, but forcing motorists to observe them is trickier... 限制车速容易，但强制司机遵守这些限速规定就难办多了。