You decide to perform a simple experiment to determine whether nitrogen or phosphorus is a more limiting nutrient in a pond in your backyard. Using a curtain that does not allow water, nutrients, or organisms to pass through, you divide your pond into four equal$-$sized quadrats $($like a pie with four pieces$).$ You randomly apply one of the following treatments to each quadrat: no nutrients $($control$),$ nitrogen only, phosphorus only, nitrogen and phosphorus. After $10$ days, you measure net primary productivity $($NPP$)$ in each quadrat of your pond. You find the following results: Control NPP $=1\mathrm{.}2g\frac{C}{m^2}\frac{?}{d}$; nitrogen only NPP $=1\mathrm{.}3g\frac{C}{m^2}\frac{?}{d}$; phosphorus only NPP $=2\mathrm{.}8g\frac{C}{m^2}\frac{?}{d}$; nitrogen and phosphorus added NPP $=2\mathrm{.}8g\frac{C}{m^2}\frac{?}{d}.$ Which is true about nutrient limitation in your pond?

Neither nutrient is limiting$.$

Nitrogen is the only limiting nutrient.

Phosphorus is the only limiting nutrient.

Nitrogen and phosphorus are both limiting nutrients.