（ ）is known to the world, Mark Twain was a great American writer.
A.正确答案AAs
B.Once
C.That
D.It
（ ）is known to the world, Mark Twain was a great American writer.
（ ）is known to the world, Mark Twain was a great American writer.
A.正确答案AAs
B.Once
C.That
D.It
