问题补充：
the boy is determined to do something , no one can stop him.
A. Even if
B. Now that
C. Once
D. However
答案：
A. Even if
B. Now that
(答案→)C. Once
D. However
解析：词义辨析题。 A. Even if即使 B. Now that 既然 C. Once 一旦D. However 然而句意：一旦这个男孩下定决心做事情没人能阻止他。 根据语境选C
