NSC / Time Deposit / SCSS

To avail the benefit of deduction u/s 80C, do the assessee need to invest in the following schemes every year or single investment in a single year is enough? -

1. National Savings Certificate
2. Time deposits
3. Senior Citizen Saving scheme

I mean if they invest in one of the schemes in the first year then do they need to repeat the investment in the next year in the same scheme? Please answer for each scheme.