Which of the following is a feature of the monastery cloister in the Middle Ages

A．It was surrounded by a river.

B．It generally had a fountain or a well at the center.

C．It was surrounded by flowers.

D．It generally had a wall at the center.

染色血涂片中红细胞明显大小不等，相差悬殊，见于( )

A．大细胞性贫血
B．小细胞性贫血
C．小细胞低色素性贫血
D．双相性贫血
E．巨幼细胞性贫血