The supply of silver in the mine had diminished, causing great concern among the people of the town.

A. disappeared

B. erupted

C. expired

D. declined

【答案解析】本题正确选项D。【译文】矿井里的银供应减少了，引起了镇上居民的极大关注。【解析】在四个备选项中，A项disappear“消失”；B项erupt“爆发，喷出”；C项expire“期满”；D项decline“下降；衰退”。题干中的画线词diminish“减少，降低”，和decline意思最接近，依据题意本题最符合的选项为D。