大学英语：By the middle of

　　1. 时态题：By the middle of the century， both radio and television had become established means of transmitting sounds and/or pictures. By the time of +现在时间状语，用一般现在时;by the time of +将来时间状语，用将来完成时;by the time of +过去时间状语，用过去完成时。

　　2. Printed materials 印刷材料;isolated areas 荒芜的地区

　　3. Entertain(v.娱乐)-entertained(adj. 娱乐的)-entertainment(n. 娱乐)

　　4. In 1975，many people in India saw television for the first time as they watched programs about agriculture and health. (因为)

　　5. Common的最高级the most common