单选题一艘轮船漏水，船中已经有水600桶，此时用两台抽水机抽水，它们的效率分别为每分钟20桶和16桶，50 min可以抽完，则轮船每分钟漏进水有( )． (A) 20桶 (B) 22桶 (C) 23桶 (D) 24桶 (E) 25桶

单选题若f’(x)＜0(a＜x≤b)且f(b)＞0，则在(a，6)内必有( ) A．f(x)＞0 B．f(x)＜0 C．f(x)=0 D．f(x)符号不定

单选题以下结论正确的是( )A．函数f(x)的导数不存在的点，一定不是f(x)的极值点B．若x0为函数f(x)的驻点，则x0必为f(x)的极值点C．若函数f(x)在点x0处有极值，且f'(x0)存在，则必有f'(x0)=0D．若函数f(x)在点x0处连续，则f'(x0)一定存在

单选题设确定了可导函数y=f(x)，则______

单选题设，则

单选题Paul and John work on ______ days. A. altering B. alternative C. alterable D. alternate

单选题在边长为1的正方形ABCD内画两条半径1的圆弧：以A为圆心的BD弧，以B为圆心的AC弧，它们的交点为E，如图所示．则曲边三角形CDE的面积为()．

单选题下列函数在指定区间上不存在定积分的是A．B．C．D．

单选题 With the US economy slowing down, layoffs are everywhere. No industry is spared. If you end up having to start over, in addition to starting your job search, there are several things you should take care of to make your transition a smooth one. First and foremost, clear up any misunderstanding about how and why you left your last job with your ex-boss. Whether you left voluntarily, were fired or were laid off due to budget cutbacks, make sure you both have the same explanation. Agree on job titles accordingly. Also ask for a reference if you think your ex-boss will offer one and you trust that he or she will speak honestly about your performance. You should have a source of emergency cash that you can use in the interim. Don't panic and liquidate your stocks and bonds just yet, be optimistic in your prospects while also be more frugal than usual. You should save money on not having to dry-clean work clothes so often and eating less take-out lunches. Save money by not eating out at restaurants and watch videos rather than going to the movies every weekend. Make a note of your job hunting expenses, such as career counselors' consulting fees and resume printing costs, and save the receipts. By next year's tax-filing time, you could get deductions on your job-search expense (unless you left a job willingly or was a college graduate looking for your first job). Most companies terminate your medical insurance coverage as soon as you stop working for them. But it doesn't mean you have to forgo medical coverage altogether. There is something called Consolidated Omnibus Budget Reconciliation Act (COBRA) in the United States that legally protects an ex-employee's right to stay in the company's health care plan. However, the company will stop paying your premiums, and you will have to pay out of your pocket the expenses. This is still a good option compared to no health insurance at all. Another important thing to take care of when you change jobs is your 401 (k) account. A 401 (k) is the retirement fund that most companies offer. It's named after section 401 (k) in the Internal Revenue Service's policy documents. You put aside a percentage of your paycheck each pay period, and the money accumulated will be managed by the 401 (k) fund manager your employer has hired and is invested in the stock market. You cannot withdraw money from this account until you reach this age, or you will incur penalties. When you leave a job, the money can sometimes be kept with your ex-employer for a while. It's always a good idea to compare your new employer's 401 (k) plan with your old one. Every company offers different types of investment options, from overseas stocks to hightech stocks and everything in between. If you do want to transfer the account to your new employer, you need to go to the human resources department and ask for forms that help you make the transition. Don't forget to ask for job leads from your ex-coworkers. Even if you are leaving for a job in another industry, you never know what people they happen to know that can help with your job search. Keep in touch with the friends you have made at your old job. Remember to anchor yourself to people, not institutions, and you will find that any transition is made easier.

单选题如果，那么=()．