Analysis of each statement:

• A: "Theta is positive for long positions in ATM options" - FALSE. Theta is negative for all long option positions because time decay works against the holder.

• B: "Gamma is large for ITM options" - FALSE. Gamma is highest for at-the-money (ATM) options and decreases for both in-the-money (ITM) and out-of-the-money (OTM) options.

• C: "Theta is negative for long positions in ATM options" - TRUE. All long option positions have negative theta due to time decay.

• D: "Delta of ITM puts tends to 1" - FALSE. Delta of ITM puts tends to -1 (negative because puts move opposite to the underlying).

Therefore, only statement C is correct.