单项选择题

A psychological issue that began to be discussed in the 1950s was the question of the most appropriate age for second language learning．The ability of young children to learn language“easily”had，from time to time，been noted in psychological literature．But in the 1950s it was the view of Penfield，a medical doctor at McGill University in Montreal， which aroused widespread attention．Partly on the basis of his scientific work as a surgeon and partly on his personal conviction，Penfield put forward the idea that childhood years offered a biological favorable stage for second language learning，and he recommended that the childhood years should be used more intensively for language training．This viewpoint， shared by a growing number of teachers，specialists，and the general public，demonstrated itself in the introduction of language teaching in the early years of schooling in several countries．The debate on this controversial issue has gone on ever since，and in spite of experimentation，some research，and endless theoretical argumentation，the issue of the best age for language learning has remained unresolved even many years after Penfield’s challenge had opened up the debate．
The need for a more systematic psychological research on language learning was fully recognized and clearly expressed by Carroll in the 1950s：“We are fundamentally ignorant of the psychology of language learning”．Carroll believed that educational psychology might provide helpful answers to pedagogy (the study of teaching methods) by carrying out research on specific questions of language learning，for example：“Should sounds and meanings be presented at the same time or one after the other？”“Can meanings be presented just as well by verbal definitions as by pictures and concrete materials？”“How can the transfer from speaking and understanding to reading be facilitated？”“Under what conditions does the use of native language delay or facilitate learning？”“When do linguistic explanations facilitate learning？”“At what rate can new materials be introduced？”Following up these and similar questions，Carroll and some of his students began to investigate a few of them．One of the most notable inquiries of that time was Carroll’s own attempt，in collaboration with a professor of Spanish，to develop a new language aptitude test．Around the same time，studies on the social psychology of language learning were initiated by an-other professor and his students at McGill University in Montreal．From about 1960，in the context of emerging followers of psycholinguistics，there was a growing interest in studying second language learning from a psychological perspective． The text is mainly about______．