______ did he do yesterday? He helped his friends. ( )
A:What
B:When
C:Where
送友人
李白
青山横北郭,白水绕东城。
此地一为别,孤蓬万里征。
浮云游子意,落日故人情。
挥手自兹去,萧萧班马鸣。
受地理位置、地形、气候等因素的影响,我国南、北方地区自然景观差异显著,据此回答以下问题。