Please answer the following question: I'm taking a test and have to guess the right answer to the question after the article. Article: Friends play an important part in our lives, and although we may take the fact of friendship for granted, we often don't clearly understand how we make friends. While we get on well with a number of people, we are usually friends with only a very few. For example, the average among students is about 6 per person. In the beginning, it much depends on how people meet, and on good first impressions. As we get to know people, we consider things like age, race, looks, economic and social status, and intelligence. Although these factors are not of the greatest importance, it is more difficult to have a good relationship with people when there is a big difference in age and background. We pay attention to actual behavior, facial expression, and the way a person speaks. Friends will stand closer together and soft voices also express friendliness, and it is because they may give the wrong signals that shy people often have difficulty in making friends. A friendly look with the wrong facial expression can turn into an unfriendly stare, and nervousness may be wrongly understood as unfriendliness. Some relationships are a result of argument and discussion, but it is usual for close friends to have the same ideas and beliefs, the same opinions and interests -- they often talk about "being on the same wavelength". The more closely involved people become, the more they depend on one another. People want to do friends favors and hate to let them down. Equally, friends have to learn to make allowances for each other, to put up with annoying habits, and to accept differences in opinion. In contrast with marriage, there are no friendship ceremonies to strengthen the relationship between two people. But the mutual support and understanding that results from shared experiences and emotions does seem to create a close and lasting relationship, which can overcome differences in background, and break down barriers of age, class or race. Question: Why should we consider such things as age and background when making friends? Options: A: Because people of different age can't have the same interest. B: Because people who enjoy different social status have nothing in common. C: Because when making friends people need know these. D: Because differences in age and background make it difficult to make friends.
A:
D