【SC精选精讲31】Navigators have known

Navigators have known for thousands of years that the ocean has variable currents, but it is only in the last half century that a reasonably clear picture has emerged of the patterns and causes of ocean currents. 

(A) a reasonably clear picture has emerged of the patterns and causes of ocean currents 

(B) a reasonably clear picture of the patterns of ocean currents and their causes have emerged  

(C) a reasonably clear picture emerged of ocean currents, their patterns and the causes of them  

(D) there have emerged a reasonably clear picture of the patterns of ocean currents and what caused them  

(E) there had emerged a reasonably clear picture of the patterns of ocean currents and their causes

技能get: 主谓一致；语序调整

A选项正常的语序是a reasonably clear picture (of the patterns and causes of ocean currents) has emerged.