According to the passage, the exchange of medical ideas between east and west started ________.

A．Baghdad was once the center of Islamic trade.
B．There was ancient Greek medical thought in the Islamic medical system.
C．European scholars began to have interest in Islamic medicine in ninth century.
D．Chinese practices of feeling the pulse began in the seventeenth century.

A．The ground is more suitable.
B．There is more space for new plants.
C．Birds and animals bring new seeds.
D．It is supported by the forest.