From his expression, we can guess that the problem maybe was quite .A. puzzled ; puzzlingB

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(答案→)A. puzzled ; puzzling
B. puzzling; puzzled
C. puzzled; puzzled
D. puzzling; puzzling
解析：考查形容词用法。Puzzled困惑的，（常修饰人）；puzzling令人困惑的（常用来形容事物）。但是look, expression等与人有关的事物仍然用puzzled等过去分词转换的形容词修饰。句意：从他困惑的表情，我们能够猜想那个问题也许非常的令人困惑。根据句意说明A正确。