It was along the Mississippi River Mark Twain spent much of his childhood.
A. how
B. which
C. that
D. where
网友回答
A. how
B. which
(答案→)C. that
D. where
解析：此句为强调句，强调状语“along the Mississippi River”还原后应为“Mark Twain spent much for his childhood along the Mississippi River.”