Step 1: Understanding the Concept.
Whether a substituent directs an incoming electrophile to the ortho/para positions or the meta position depends on how it affects electron density around the ring, mainly through resonance and induction.
Step 2: Key Approach.
Ask one question for each group: does it have a lone pair or pi system that can donate into the ring by resonance? If yes, it is usually an ortho/para director even if it also withdraws inductively. If no, and it only withdraws electron density, it is a meta director.
Step 3: Detailed Explanation.
\( \text{NH}_2 \) and \( \text{NHCH}_3 \) both carry a nitrogen lone pair that resonates into the ring, so they push electron density to ortho and para positions and are strong ortho/para directors.
\( F \) also has lone pairs on the fluorine atom that resonate into the ring, and even though fluorine is inductively electron-withdrawing, this resonance donation wins out for directing purposes, so it too is an ortho/para director.
\( \text{CF}_3 \) is different because its carbon has no lone pair and is bonded only to three highly electronegative fluorine atoms, so it can only pull electron density away through induction, with nothing to donate back by resonance.
This leaves the meta position as the site with the least electron depletion, making it the position where electrophilic substitution actually occurs.
Step 4: Final Answer.
The meta directing group among the options is \( \text{CF}_3 \).