Many early Europeans, ________ the earth to be flat, feared that Columbus would fall off the edge of the earth.

A．believing

B．having believed

C．believed

D．to believe

某急性白血病患者化疗期间，血小板计数下降为15×10⁹/L，护士对其进行护理时，最应警惕的表现是 （）

A.发热

B.咳嗽

C.肛周疼痛

D.剧烈头痛

E.皮肤出血点增多