In my opinion, keeping dogs well up is advisable for dog owners.
A. to tie
B. being tied
C. tied
D. to be tied
网友回答
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。