Below are given some sentences out of which the sentence numbered 4 has been correctly placed. The rest of the sentences A, B, C, D, E, F need to be arranged correctly in order to form a logical order.

A. The terms "popular music" and "pop music" are often used interchangeably, although the former describes all music that is popular and includes many diverse styles.

B. "Pop" and "rock" were roughly synonymous terms until the late 1960s when they became increasingly differentiated from each other.

C. Pop music is a genre of popular music that originated in its modern form in the United States and the United Kingdom during the mid-1950s.

4. Although much of the music that appears on record charts is seen as pop music, the genre is distinct from chart music.

D. These core elements include generally short to medium-length songs written in a basic format, as well as the common use of repeated choruses, melodic tunes, and hooks.

E. Pop music is eclectic, and often borrows elements from other styles such as urban, dance, rock, Latin and country. 

F. Nonetheless, there are certain core elements that define pop music.