Questions 51 to 55 are based on the following passage: In 1964, the world coined a new word, Beatle-mania. That year the world was introduced to four Englishmen named John, Paul, George, and Ringo. For the next eight years, these four were the number one musical group. Each new album that appeared was a success, but the 1967 album called Sgt. Pepper’s Lonely Hearts Club Band was a milestone. It indicated a turning point in their music. The music of the Beatles from 1964 to 1967 dealt with traditional love themes. All their songs from 1964 tell of happy meetings between boy and girl, the beginning of love. By 1966, the love affair isn’t moving smoothly. In the 1966 song "No Reply", the situation goes like this: "You" walked hand in hand with another man in my place. Yet the unfaithful love is part of the traditional love theme. The Beatles were still concerned almost totally with love in early 1967. Then came the Sgt. Pepper album. From the 1967 Sgt. Pepper album until their final album in 1972, the Beatles experimented with themes other than the traditional love theme. Interest in drugs replaced interest in love, and the very popular song "Revolution", from 1970, introduces a political theme to the music. The final theme in Beatles’ music is almost religious in tone. The Beatles had come far from the traditional theme of love. During their eight years, the Beatles produced fifteen albums and over one hundred songs. The Beatles’ music, with its variety of themes, not only reflected the times extremely well but also became a musical force. Their impact is still felt in and out of the music world.

From this passage we know that （）.