【单选题】
In order to prepare a lecture, one must do a lot of research
and spend plenty of time____ his material so that his speech
is clear and easy to follow.
【单选题】
、Although he had looked through all the reference material on the subject, he still found it hard to understand this point and her explanation only ____ to his confusion.
【单选题】
As a great innovator in American literature, Walt Whitman wrote his poetry in an unconventional style which is now called free verse, which is ______.
① lyrical poetry with chanting refrains
② poetry without a fixed beat or regular rhyme scheme
③ poetry without rhymes at the end of the lines but with a fixed beat
④ poetry in an irregular metric form and expressing noble feelings