2。1 Second Language Acquisition Theory

Language acquisition is one's language learning and development。 The first language acquisition refers to the learning of mother tongue, while the second language acquisition refers to the learning of the second language or foreign language。 Many linguists have different hypotheses about the Second Language Acquisition。 Rob Ellis (1997:349) reported on the mechanism of language acquisition by Gass flow charts。 He believes that the steps of information entering the brain are as follows: attention, input, understanding, comprehensible input, intake, implicit knowledge and explicit knowledge。 Facts have proved that the second language skills mainly come from implicit knowledge and explicit knowledge。 Explicit knowledge refers to the rules of language that exist in people's minds。 It can consciously monitor people's language formation。 Implicit knowledge is the psychological representation of linguistic rules。 It is the grammar internalized by language learners。 The results of implicit knowledge can be achieved through classroom teaching and practice, but largely depend on the amount of linguistic exposures, including input and output。 Implicit  knowledge is acquired mainly through communication with target language。 Therefore, it is necessary to combine teaching with language structure and language function。