D. 1,200
This is because if it takes 1 and a half hours **1.5** to travel through city a and city b , and the plane goes 800km per hour and 400km is half of that it then the answer has to be d.
Answer:
fertilizers
Explanation:
Plants use nitrates as a supply of nitrogen, which is needed to make proteins for healthy growth. Plants absorb nitrates in water through their roots. Nitrates are present in high levels in plant fertilisers. Without nitrates, the amount of chlorophyll in leaves reduces.