关于通电直导线在磁场中所受的安培力，下列说法中正确的是 

A．通电直导线在磁场中一定受到安培力的作用

B．安培力大小仅与磁感应强度、电流大小成正比，而与其他量无关

C．安培力的方向不一定垂直于通电直导线

D．安培力的方向总是垂直于磁场和通电直导线所构成的平面

In every cultivated language, there are two great classes of words which, taken together, comprise the whole vocabulary. First, there are those words（1）which we become acquainted in daily conversation, which we（2）,that is to say, from the（3） of our own family and from our familiar associates, and（4） we should know and use （5 ）we could not read or write. They （6） the common things of life, and are the stock in trade of all who （7） the language. Such words may be called“popular”, since they belong to the people （8） and are not the exclusive （9） of a limited class. On the other hand, our language （10） a multitude of words which are comparatively （11） used in ordinary conversation. Their meanings are known to every educated person, but there is little （12） to use them at home or in the market-place. Our （13） acquaintance with them comes not from our mother's （14） or from the talk of our school-mates, （15） from books that we read, lectures that we （16） ,or the more （17）conversation of highly educated speakers who are discussing some particular （18） n a style appropriately elevated above the habitual（19） f everyday life. Such words are called“learned”, and the （20） between them and the“popular”words is of great importance to a right understanding of linguistic process.

请在16处填上正确答案（）

A.hear of

B.attend

C.hear from

D.listen