乙醇作为片剂润湿剂时常用浓度是（）
A.20%以下
B.30%～50%
C.50%～80%
D.30%～70%
E.60%～80%
参考答案：D
根据句子意思和首字母提示完成单词 (10分)
小题1:Don’t read in the sun. It does great h_________ to your eyes.
小题2:It is polite to wait in the l_________ when you are waiting to buy tickets.
小题3:My friends gave me a lot of g_______ on my birthday.
小题4:He feels l_________ from time to time because he misses his old friends.
小题5:I didn’t know it was you. You have c________ a lot.
为了提高网络可靠性和生存性，规范定义了EPON系统中可采用光链路保护倒换的4种模式，请描述只涉及OLT设备的两种光链路保护模式（模式a和模式b）。
