A、They should be effective in most situations. B、They should be based on translation and grammar. C、They should be used to teach

W: Good morning, Dr. Harley. Thank you very much for coming on our radio talk. We know that you are an applied linguist specializing in second language acquisition. Could you please tell us what second language acquisition is?
M: Well, second language acquisition is that…it happens when a child or adult has already become competent at a language, and then they attempt to learn another.
W: Most people think it is difficult to learn another language. What are the reasons?
M: There are a number of reasons. First, research studies have shown that some aspects of language learning especially grammar are more difficult beyond a certain age, say, after around 12 years of age.
W: So age plays an important role in language learning.
M: Yes. But that’s not the only reason. For example, time and interest. Old children and adults often have less time and motivation to learn a second language. Besides, we find that learners will experience difficulty when their mother tongue and the second language they are learning differ.
W: Perhaps this is the key issue. Differences between languages cause language learning problems.
M: This may be one of the issues, but this cannot be the whole story, as not all differences between languages cause difficulty. Research has found that many Czech speakers learning English were puzzled by grammatical constructions in which the two languages do not differ.
W: Oh, really? The picture is more complicated than we’ve imagined.
M: Definitely yes. Each language learning situation is different. So reasons vary a lot from case to case.
W: Dr. Harley, since learning a second language is a difficult process, are there any methods to teach a second language?
M: There again. No method is absolutely effective in all situations. I mean, it all depends on specific conditions. But generally speaking, there are a number of methods that have been used to teach a second language.
W: Could you mention one?
M: For instance, there is the traditional method. This method is based on translation from one language to another and emphasizes grammar teaching.
Questions 1 to 4 are based on the conversation you have just heard.
1. What are the two speakers mainly talking about?
2. Why is it difficult for old children and adults to learn another language?
3. What can we learn about Czech and English?
4. What does the man think of second language teaching methods？