by many well-known experts and film stars, the product was very popular at one time.
A. To advocate
B. Having advocated
C. Advocating
D. Advocated
网友回答
A. To advocate
B. Having advocated
C. Advocating
(答案→)D. Advocated
解析：考查非谓语动词，主语the product与advocate之间是动宾关系，所以用过去分词advocated，句意：这种产品被许多的著名专家和电影明星所拥护，曾经非常受欢迎。所以选D。