This is why I hate the new exams, if you misinterpret the question it can leave you blank. It says that the solution was alkaline, so we assume alkaline solution was the high concentration, yet the cells are pink, from the question it says that the indicator turns red if acid is detected. Since there is a high concentration of alkaline in the solution, there is a low concentration of acid in the solution. This means that acid moved from low concentration which is the liquid into the cells, and active transport is moving against the concentration gradient (From low concentration to high concentration), so active transport is the answer.
As for carrier proteins, there is no mention of ions or charged particles involved, so it can't be channel proteins, therefore it is carrier proteins.
I had to read the question 3 times before finally getting it, these examiners sure know how to throw you off.