1a negative result of monoculture farming
a. a resistance to pesticides
b. an increase in crop prices
c. a decrease in mineral nutrients in soil
d. a decrease in the number of diseases

A negative result of monoculture farming is a decrease in mineral nutrients in soil.

Explanation:

When only one type of crop or plant variety is grown in a farming land at a certain period of time, it refers to Mono culture. It is a farming technique that is used industrial and also in organic way of farming.  It is an efficient way for harvesting a particular species based on the season that supports their growth. The same way it also has disadvantages too. It can introduce many number of diseases and pests in the farming land.  

The process of planting and harvesting the same plant variety in an area over a period of time will lead to the removal of nutrients that are present in that particular area. This is because the all the plants will be dependent on the same type of nutrients present in the soil and they will take that type abundantly. This will result in the eradication of that nutrient type from the soil resulting in making the soil very weak. Hence that farm area will not be suitable for growing other crops in a healthier way. This will lead to the use of fertilizers by the farmers that will again eradicate the soil nutrients.