视觉最为敏锐的部位是（）
A.视神经 * *
B.中央凹
C.视网膜盲部
D.玻璃膜
E.角膜
参考答案：B
龟、鹤共有100个头，鹤腿比龟腿多20只．问：龟、鹤各几只？
—Do you like your new teacher?
—Of course. She is friendly _____ us. [ ]
A. to
B. of
C. for
D. with
