Passage 2
In the first half of the twenticth century, many psychologists believed that only externally observable,__(16)__ behavior was relevant for study because the internal cognitive mechanisms that underliebehavior could not be __(17)__ scientifically. These psychologists__(18)__ influenced the waylinguists and language educators viewed language. Language teachers believed that the mechanismbehind language learning was habit formation, by which a linguistic behavior became conditioned to aparticular stimulus and then generalized to other similar stimuli. The knowledge of a languageconsisted of a set of habits demonstrated by the language user._(19)_. this view, learning a secondlanguage essentially cqualed learning a new sct of habits. That is to say, language knowledge was __(20)__a set of linguistic habits, and learning a second language simply meant replacing one set ofhabits with another.
【題組】16.
(A)limbo
(B)outward
(C) backflash
(D) excerpt