Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the questions from 35 to 42

Whether it's the melodic sound of an Eric Clapton solo or the growl of a heavy metal band, the electric guitar has influenced popular music and culture more than any other instrument. Rock's greatest musicians have always been closely identified with their guitars. But the instruments being designed for tomorrow's pop stars may look and sound rather different from today's familiar electric and acoustic guitars.

It is only sixty years since the electric guitar was invented. Since then there have been incredible changes to the technical design of the instrument. From what was once a rounded wooden box with a hole in the front, the guitar has evolved into the smooth solid body of the rock guitarist's "axe”. The most modern guitars are really computer-controlled synthesizers.

Adolph Rickenbacker's Electro String Company produced the first world's first electric guitar. It was made of wood and played on the user's lap. The first real breakthrough in design came in 1950 when Leo Fender, a California radio repairman, made the first solid-bodied electric guitar, the Fender Telecaster. Soon after the inventor Les Paul made the famous Gibson Les Paul, Fender launched his stylish Stratocaster two years later. These guitars became standard instruments against which newer guitar designs are measured.

All sorts of different materials have been used to make guitars. Acoustic guitars are made from wood, which gives a soft tone. Wood is also a popular material in electric guitar manufacture, but more modern materials such as glass and carbon fiber are also used. There have also been guitars with metal bodies and necks though these were never popular with players, who claim metal feels cold in the hand.

Plastics, on the other hand, have been more used in guitar bodies. A company that makes parts for the aerospace industry has begun to use a kind of fiberglass that was originally used in helicopter blades to make the bodies for its electric-acoustic instruments. Other makers have begun to experiment with graphite, which is ten times stiffer than wood but much lighter. It doesn't expand or contract as the temperature or humidity changes either. This makes it particularly suitable for guitar necks and for tennis rackets, for which it is also used.

As long as scientists and musicians work together harmoniously, the electric guitar will continue to benefit from technological innovations. But for all the efforts of the guitar companies' design engineers, managers and quality controllers, it's the musicians who finally make the instruments sing - and not necessarily in the way the guitar maker intended.

What is likely to change in the future?

This class, ___________ is a prerequisite for microbiology, is so difficult that I would rather