I haven't seen Anna since she left our hometown two years ago, but we do keep in touch with each other

by sending emails ________.[ ]

A．here and there  

B．sooner or later

C．at one time  

D．now and then

溶血反应时出现黄疸和血红蛋白尿的机制是()

A．红细胞凝集成团，阻塞部分血管

B．凝集的红细胞发生溶解，大量血红蛋白释放入血浆

C．血红蛋白变成结晶体，阻塞肾小管

D．肾小管皮质缺血、缺氧而坏死脱落

E．红细胞破坏释放凝血物质引起DIC