单选题设处连续，则f(x)在x=0处()

单选题下列结论正确的是(A)若函数f(x)在[a，b]上可积，则f(x)在[a，b]上必有界；反之，若函数f(x)在[a，b]上有界，则f(x)在[a，b]上必可积．(B)若函数f(x)在[a，b]上可积，则f(x)在[a，b]内必定有原函数；反之，若函数f(x)在[a，b]内有原函数，则f(x)在[a，b]上必定可积．(C)若函数f(x)在任何有限区问上可积，则对任一点c，有(D)若函数f(x)在[a，b]上可积，则必存在ξ∈[a，b]，使得

单选题下列命题正确的是(A)若D为有界闭区域，L为其边界曲线正向，则总有格林公式(B)若，则曲线积分必定与积分路径无关，可以选择平行于坐标轴的折线段作为积分路径以简化运算．(C)若在区域D内总有，则对于D内任意一条封闭曲线L，总有(D)若在单连通区域G内，P(x，y)，Q(x，y)有一阶连续偏导数，且P(x，y)dx+Q(x，y)dy为函数u(x，y)的全微分的充分必要条件为在G内恒成立．此时u(x，y)总可以表示为或或其中(x0，y0)为G内任一确定点．

单选题设sinxln|x|是f(x)的一个原函数，则不定积分∫xf"(x)dx=A．B．xcosxln|x|+sinx-sinxln|x|+C．C．D．以上均不正确．

单选题设f(x)在x=a处二阶可导，则等于______．A．-f"(a)B．f"(a)C．2f"(a)D．

单选题Until recently, mobile radio was to wireless communications what the Yugo was to transportation. With a mixed clientele ranging from truckers using CBs to police armed with walkie-talkies to taxi drivers dispatched by radio, it was viewed as an unglamorous business and a technological backwater. But specialized mobile radio, as it is known, has been rediscovered. It is now considered one of the biggest prizes in the all-out war for the public airwaves. The reason: high-tech companies have figured out how to profitably rebuild the antiquated dispatching system into an advanced cellular-telephone network that can take on the likes of AT & T and the giant Baby Bells. Upstart Nextel Communications sent shock waves through the industry last week when it agreed to buy Motorola's SMR frequencies for $1.8 billion. That could pose a serious threat to cellular hegemony. Although both systems are based on the same basic technology, SMR systems are digital and cover almost 25 times as much area as the average cellular network. SMR handsets won't work on cellular systems and tend to be bulkier than cellular phones, though they provide more features, like a digital pager service. And while cellular growth has tripled to some 13 million subscribers since 2000, the technology has been losing ground. It is running out of channel capacity so fast, in fact, that 40% of cellular calls in high-density areas like Manhattan and Los Angeles fail to be completed. SMRs have capacity to spare, and service could eventually be priced 10% to 15% less than cellular. Dispatchers predict they will have at least 10 million subscribers by the end of the decade. There are now about 1.5 million users of SMRs. The addition of another contender to an already crowded field of telephone systems will surely multiply the confusion. By the year 2010, consumers will be able to choose from at least half a dozen vendors of a dizzying array of wireless-communications services, including pagers, voice mail answering machines and cellular phones. Phone and cable television operators, such as Bell South, MCI and Cox Enterprises, are developing so-called personal communications networks, or PCNs, a highly advanced portable-phone system that is expected to cover a wider area, connect to a greater variety of services and be cheaper to operate than conventional cellular. And many companies that have gambled on the wrong technological standards, and invested billions trying to develop the same markets, will undoubtedly lose a great deal of money before the shakeout is over. "The winners," says Nextel chairman Morgan O'Brien, "will be those who can make the choice for consumers easy." With all the anticipated confusion--mindful of the early years of personal computers--it is likely to be years before anyone calls the purchase of wireless products an "easy" choice.

单选题将函数分别展成余弦级数和正弦级数，则当n→∞时，A．an是的高阶无穷小，bn是无穷小．B．an是的高阶无穷小，bn是的高阶无穷小C．bn是的高阶无穷小，an是无穷小．D．bn是的高阶无穷小，an是的高阶无穷小

单选题设向量组(Ⅰ)：α1，α2，…，αs，其秩为r1，向量组(Ⅱ)：β1，β2，…，βs，其秩为r2，且βi(i=1，2，…，s)均可以由α1，…，αs线性表示，则______．

单选题设A为m×n矩阵，C是n阶可逆矩阵，矩阵A的秩为r，矩阵B=AC的秩为r 1 ，则

单选题设f(x)在[a，b]有连续导数，x0∈(a，b)是f(x)在(a，b)的唯一驻点，又f'(a)＞0，f'(b)＜0，则点x=x0是 (A) f(x)的极小值点． (B) f(x)在[a，b]的最小值点． (C) f(x)在[a，b]的最大值点． (D) f(x)的极大值点，但不是f(x)在[a，b]的最大值点．

单选题下列命题正确的是(A)若收敛，则条件收敛．(B)若，则收敛．(C)若收敛，则收敛．(D)若绝对收敛，则收敛．