选a是什么道理啊? 多谢解答
Q31:
Which of the following most logically completes the argument below?
Davison River farmers are currently deciding between planting winter wheat this fall or spring wheat next spring. Winter wheat and spring wheat are usually about equally profitable. Because of new government restrictions on the use of Davison River water for irrigation, per acre yields for winter wheat, though not for spring wheat, would be much lower than average. Therefore, planting spring wheat will be more profitable than planting winter wheat, since‗‗‗‗‗‗.
the smaller-than-average size of a winter wheat harvest this year would not be compensated for by higher winter wheat prices
new crops of spring wheat must be planted earlier than the time at which standing crops of winter wheat are ready to be harvested
the spring wheat that farmers in the Davison River region plant is well adapted to the soil of the region
spring wheat has uses that are different from those of winter wheat
planting spring wheat is more profitable than planting certain other crops, such as rye | 
