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【单选题】
What were people doing in China and the Middle East as far back as 5000 BC?A.
They were exchanging metals for goods.
B.
They were exchanging one item for another.
C.
They were using salts to purchase goods.
D.
They were using coins as money.
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皮皮学刷刷变学霸
举一反三
【单选题】设f(x)在x=a点可导，则|f(x)|在x=a不可导的一个充分条件是( )．
A.
f(a)=0，f'(a)=0
B.
f(a)=0,f'(a)≠0
C.
f(a)＞0，f'(a)＞0
D.
f(a)＜0，f'(a)＜0
【简答题】( )是消费者的购物凭证,也是( )的基础和依据。
【单选题】设函数f(x)在点x=a处可导，则甬数｜f(x)｜在点x=a处不可导的充分条件是( )．
【单选题】甲砂场将应发给乙建筑公司的2500m3细砂发给了丙路桥公司，3d后，甲砂场向丙路桥公司索取这批细砂。所产生的债权债务关系是（ ）之债。
A.
合同
B.
侵权
C.
无因管理
D.
不当得利
【单选题】设函数f(x)在点x＝a处可导，则函数｜f(x)｜在点x＝a处不可导的充分条件是( )．
A.
f(a)＝0且fˊ(a)＝0
B.
f(a)＝0且fˊ(a)≠0
C.
f(a)＞0且fˊ(a)＞0
D.
f(a)＜0且fˊ(a)＜0
【单选题】How did Franklin help George Washington?
A.
He provided Washington with a lot of money.
B.
He persuaded France to support Washington.
C.
He served as a general in Washington's army.
D.
He represented Washington in negotiations with Britain.
【单选题】The battle of Trenton was very important to Washington because______.
A.
it gave Washington the victory he needed
B.
it was his last battle as a general
C.
he defeated all the British soldiers
D.
it won the war for American independence
相关题目：
【单选题】设函数f(x)在点x=a处可导，则甬数｜f(x)｜在点x=a处不可导的充分条件是( )．
【单选题】甲砂场将应发给乙建筑公司的2500m3细砂发给了丙路桥公司，3d后，甲砂场向丙路桥公司索取这批细砂。所产生的债权债务关系是（ ）之债。
A.
合同
B.
侵权
C.
无因管理
D.
不当得利