The result might not as satisfactory as expected but the on his face told us that he was

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(答案→)A. expression
B. impression
C. celebration
D. appearance
解析：A. expression表达，表情，B. impression印象，C. celebration庆祝，D. appearance出现，外貌，句意：结果不想预想的那样令人满意，但是他脸上的表情告诉我们他很高兴。根据句意选A。