为支援雅安灾区，某学校计划用“义捐义卖”活动中筹集的部分资金用于购买A，B两种型号的学习用品共1000件，已知A型学习用品的单价为20元，B型学习用品的单价为30元．

（1）若购买这批学习用品用了26000元，则购买A，B两种学习用品各多少件？

（2）若购买这批学习用品的钱不超过28000元，则最多购买B型学习用品多少件？

Financial derivatives contribute to market completeness because:()

A. the market with financial derivatives allows traders to more exactly shape the risk return characteristics of their portfolios. 

B. it is a market in which the owner of an option has the right to purchase the underlying good at a specific price, and this right lasts until a specific date. 

C. it is a market in which any and all identifiable payoffs can be obtained by trading the securities available in the market.