The correct answer is: I don’t think I’ll play tennis (today).
The other options are incorrect because they do not reflect the speaker’s current intention. The speaker has already arranged to play tennis today, but now they have decided that they don’t want to play. This means that they have not played tennis yet, and they do not plan to play tennis in the future.
Option A is incorrect because it states that the speaker has already played tennis today. This is not the case, as the speaker has just decided that they do not want to play.
Option B is incorrect because it states that the speaker played tennis today. This is also not the case, as the speaker has just decided that they do not want to play.
Option C is incorrect because it states that the speaker will play tennis today. This is not the case, as the speaker has just decided that they do not want to play.
Option D is incorrect because it states that the speaker will be playing tennis today. This is also not the case, as the speaker has just decided that they do not want to play.