请问关于句子中的定语从句
Medical researchers are painful aware that there are many problem to which they have not found solution so far
麻烦请给我讲解一下句中 "to which"是不是用来修饰前面的problem用的.to是 solution to 将介词to 提前.实际应该是 solution to problems.能不能有高人给我再讲解的细一些,我对从句的掌握不太好