GWD - 1 Q30

The ancient Anasazi harvested such native desert vegetation as the purple-flowered bee plant, what they now commonly call wild spinach in northern Arizona and other parts of the southwestern United States.

1. what they
                   （指代不清）
                   now commonly call

2. a plant that they
                   （指代不清） now commonly call

3. now commonly called

4. and
                    is
                   （逻辑主语是Anasazi，但实际要的主语是the purple-flowered bee plant）
                   now commonly called

5. which it
                       (多余)
                   is now commonly called

正确答案是C, 但是实在不是很清楚, C 这个答案怎么看起来想不完整的句子能? 我自己选的是D, 其实也不是决的很对. 可以帮助分析一下这句子的主谓到地是什么,看起来所有答案都怪怪的....谢谢谢谢!!!!!!!