问一道PREP DS题，少许概念不是很清楚。。。

For Manufacturer M, the cost C of producing x units of its product per month is given by C = kx + t, where C is in dollars and k and t are constants.  Last month, if Manufacturer M produced 1,000 units of its product and sold all the units for k + 60 dollars each, what was Manufacturer M's gross profit on the 1,000 units?

(1)  Last month, Manufacturer M's revenue from the sale of the 1,000 units was $150,000.

(2)  Manufacturer M's cost of producing 500 units in a month is $45,000 less than its cost of producing 1,000 units in a month. 

answer E

gross profit , cost , revenue ，还有销售额，这几个词之家的关系有点弄不清，尤其gross profit和revenue，没学过会计，麻烦NN帮我理一下这几个概念。。。

要算出这个gross profit就需要知道t

但是两个条件都算不出t，所以选E