Gilbert formulated this famous theory. This theory is now widely applied in language teaching. (relative clause)
【正确答案】：Gilbert formulated this famous theory which is now widely applied in language teaching.
【题目解析】：relative clause就是定语从句。将两个句子合成一个包含定语从句的句子，具体做法就是：将其中一句用关系词替换了名词后，作为另外一句的修饰语既可。
