Select the best transformation from past to present tense



They thought they had found the thief, but they were mistaken.

 They think they has found the thief, but they are mistaken.

"They think they have found the thief, but they are mistaken.

He told me he thought prices were going up.

(a) He tells me he thinking prices are going up.

(b) He tells me he thinks prices are going up.

She said she couldn't understand what I meant.

(a) She says she can’t understands what I mean.

(b) She says she can’t understand what I mean.