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【单选题】
设平面区域【图片】为单连通的开区域，函数【图片】、【图片】在【图片】内具有一阶连续偏导数，则曲线积分【图片】在【图片】内与路径无关的充分必要条件是（ ）A.
，
B.
区域 内任一条闭合曲线 C ，有
C.
存在一个二元函数 ，使得
D.
以上答案都正确。
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【单选题】投资项目可行性研究报告应达到一定的深度要求。下列关于投资项目可行性研究深度的说法，正确的是( )。
A.
可行性研究确定的融资方案应能满足银行等金融机构信贷决策的需要
B.
可行性研究选用的主要设备应附有与供货商签订的合同
C.
可行性研究报告应明确提出项目可行的结论
D.
可行性研究阶段对生产成本的估算应首选指标估算法
【单选题】【单选】Depths in the routes (Malacca and Singapore Straits) vary between20m and about 23m but there are many areas of sandwaves and depths are liable to change. The statement infers that____.
A.
depths in malacca and Singapore Straits are stable
B.
depths in malacca and Singapore Straits are changeable
C.
depths in malacca and Singapore Straits are invariable
D.
depths in malacca and Singapore Straits are the same all the time
【单选题】Depths in the routes (Malacca and Singapore Straits) vary between 20m and about 23m but there are many areas of sandwaves and depths are liable to change. The statement infers that .
A.
depths in Malacca and Singapore Straits are the same all the time
B.
depths in Malacca and Singapore Straits are stable
C.
depths in Malacca and Singapore Straits are invariable
D.
depths in Malacca and Singapore Straits are changeable
【单选题】Depths in the routes (Malacca and Singapore Straits) vary between 20m and about 23m but there are many areas of sand waves and depths are liable to change. The statement infers that _____.
A.
depths in Malacca and Singapore Straits are stable
B.
depths in Malacca and Singapore Straits are changeable
C.
depths in Malacca and Singapore Straits are invariable
D.
depths in Malacca and Singapore Straits are
【简答题】I picked up the bag to protect my face from the smoke and heat.英译汉
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