13.__ is known to the world, Mark Twain was a great American writer.
A、As
B、 Once
C、That
D、It
Ⅱ. Vocabulary and Structure ( 15 points ) Directions : There are 15 incomplete sentences in this section. For each sentence there are four choices marked A, B, C and D. Choose one answer that best completes the sentence and blacken the corresponding letter on the Answer Sheet. 6. Jonathan and Joe left the house to go for__ after supper.