In my opinion keeping dogs well up is advisable for dog owners.A. to tieB. being tiedC.

问题补充：

In my opinion, keeping dogs well up is advisable for dog owners.

A. to tie

B. being tied

C. tied

D. to be tied

答案：

A. to tie

B. being tied

(答案→)C. tied

D. to be tied

解析：C 考察非谓语动词。句义：我认为，狗的主人应该把狗拴好。Tie和句子主语之间满意连词，使用非谓语动词，且tie与逻辑主语dogs构成被动关系，使用过去分词。故C正确。