题目内容：
根据材料，回答问题。C
Nearly all “shed reading” courses have a “pacing” elementmsome timing device which lets the student know how many words a minute he is reading．You can do this simply by looking at your watch every 5 0r 10 minutes and noting down the page number you have reached．Check the averagenumber of words per page for the particular book you are reading．How do you know when 5 minutes has passed on your watch if you are busy reading the book? Well．this is difficult at first．A friend can help by timing you over a set period，or you call read within hearing distance of a pubic clock which strikes the quarter hours．Pace yourself every three or four days，always with the same kind of easy，general interest books．You should soon notice your accustomed w．P．m．rate creeping up．Obviously there is little point in increasing your w．P．m．rate if you do not undersmnd what you are reading．When you are consciously trying to increase your reading speed，stop after every chapter(if you are reading a novel)or every section or group of ten or twelve pages(if it is a text-book)and ask yourself a few questions about what you have been reading．If you find you have lost the thread of the story，or you cannot remember clearly the details of what was said．reread the section or chapter．
You can also try “lightning speed” exercise from time to time．Take four or five pages of the general interest book you happen to be reading and read them as fast as you possibly can．Do not bother about whether you understand or not．Now go back and read them at what you feel to be your “normal” w．P．m．rate，the rate at which you call comfortably understand．After a “lightning speed” reading through(probably 600 w．P．m．)you will usually find that your “normal ”speed has increased-perhaps by as much as 50—100 w．P．m．This is the technique sportsmen use when they usually run further in training than they Will have to on the day of the big race．
According to the passage，a“pacing”device________． A．is used to time the student’s reading speed
B．is not used in most speed reading courses
C．is used as an aid to vocabulary learning
D．should be used whenever we read alone
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