........"第一题，由and平行结构踢掉a&d，由主句应用一般虚拟语气，踢掉b，剩下b&e，因为b中的they指代有问题，所以最后只剩下e。
第二题，由于grow&be指代的主语有错误，所以排除b&c，grow as big as 30 feet long 不符合语法习惯应改为grow as long as 30 feet，踢掉d，再由于and it is的it可以删除，直接用and is会更加简洁。故选a"...........
I think you are pretty wrong when explaining the first question. "第一题，由and平行结构踢掉a&d，" Have you noted what is "economical determinants"? it should be "economic determinants" for sure. Welcome to comment. | 
