桂枝加大黄汤的药物组成是( )
A. 桂枝汤原方加大黄
B. 桂枝汤中芍药加量,再加大黄
C. 桂枝汤去芍药,加大黄
D. 桂枝汤中桂枝加量,再加大黄
E. 桂枝去甘草,加大黄
List thedifferences between LD and LED.
Give the structure of optical transmitter with external modulation.
Explain external modulationof optical transmission system.