题目

Galileo _____ much unfair treatment in his lifetime, but his achievements in science have long been recognized. A．had suffered         B．has suffered           C．suffers         D．suffered 答案：D在生态系统中，能充当生产者的微生物是（ ）A.乳酸菌类B.肺炎双球菌C.根瘤菌D.硝化细菌