Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 19 to 23.

In Britain, greetings cards are sold in chain stores and supermarkets, in news agents‘ shops, corner shops and, increasingly, in shops that specialize in the sale of cards and paper for wrapping presents in.

The most common cards are birthday and Christmas fiords. Many Christmas cards are sold in aid of charity and special charity card shops are often set up in temporary premises in the weeks before Christmas. A wide variety of birthday cards is available to cater for different ages and tastes. Some, especially ones for young children or for people celebrating a particular birthday, have the person‘s age on the front. Many have comic, often risque, messages printed on them, and cartoon-style illustrations. Others are more sober, with reproductions of famous paintings or attractive original designs. The usual greeting on a birthday car d is Happy Birthday‘, Many Happy Returns‘ or Best Wishes for a Happy Birthday‘.

Some people also send special cards for Easter and New Year. Easter cards either portray images of spring, such as chicks, eggs, lambs, spring flowers, etc, or have a religious theme.

Cards are produced for every “milestone‟ in a person‘s life. There are special cards for an engagement, a marriage, a new home, a birth, success in an examination, retirement, a death in the family, etc. Some are good luck‘ or congratulations‘ cards. Others, for example get well‘ cards for people who are ill, express sympathy.

(Extracted from The Oxford Advanced Learner‘s Encyclopedic Dictionary)

Scientists have proposed a possible ________ to the problem of global warming.