Don’t waste your time or energy on such a subject. Try to find something ______ researching into.

worthy of 值得...的，如果选C ，应该是Worthy of being researched into.
valuable 形容词。贵重的, 有价值的, 颇有价值的；
worthwhile 形容词。值得做的, 值得出力的，请看例句：
It's worthwhile taking the trouble to explain a job fully to new employees. 给新雇员详细讲解工作要求，费点事也是值得的。

因该选A

C
形容词
值得的

A