多数患者闪光视网膜电图正常（）
A.Stargardt病
B.Best病
C.锥体营养障碍症
D.视网膜色素变性
E.视网膜劈裂症
参考答案：A
Laura _____ in this school since she came to China. [ ]
A. is studying
B. was studying
C. will study
D. has studied
晶体三极管有NPN型和（）型两种
