Leaving the market place,the fat man looked pleased ___ himself ___ having discovered a bargain.

be pleased at sth

pleased with (惯用，排除AB)
at (“在”的意思，at having discovered a bargain.在他发现便宜货时）
for 表目的，不符，所以选D

C,答案有误，根据句子意思C更为准确。
由于捡了便宜，这个胖子在离开集市的时候显得很满意。