请教几道数学题

A certain business produced x rakes each month form November through February and shipped x/2 rakes at the beginning of each month from March through October.  The business paid no storage costs for the rakes from November through February, but it paid storage costs of $0.10 per rake each month from March through October for the rakes that had not been shipped.  In terms of x, what was the total storage cost, in dollars, that the business paid for the rakes for the 12 months form November through October?

A.     0.40x

B.     1.20x

C.     1.40x

D.     1.60x

E.      3.20x

1. 选C。11月至2月，每月生产x，则共生产4x。3月至10月，每月shipped x/2，则3月存货为3.5x，4月存货为3x，...，9月存货为0.5x，10月存货为0。11月至2月存货不计成本，3月至10月存货单价成本为$0.10，则所求存货和为$0.10(3.5x+3x+...+0.5x)=$0.10*14=$1.40x

2. 选D。由题干可知选出的3人不能是夫妻，因此第一步，先从5对夫妻中选出3对，即C(5,3)=10；第二步，从每对夫妻中选出一人，即C(2,1)*C(2,1)*C(2,1)=2^3=8。按步骤求解，应计算各步骤之积，即应有10*8=80种可能性。

多谢！！！