单选题 ①When selecting a nest

单选题. ①Exotic insect pests can produce both short-and long-term effects on forest ecosystems. ②Short-term effects include the disturbances directly associated with the action of the pest, which may cause the defoliation, loss of vigor, or death of trees. ③Long-term effects involve changes in tree species composition and the consequent alterations of forest structure, productivity, and nutrient uptake. ④Exotic pests are more efficient than most abiotic disturbances (e.g., fire or wind) at producing long-term changes in species composition. ⑤Pests often target specific tree species and, if they become established, they usually remain as permanent components of the ecosystem. ⑥Shifts in forest species composition ramify through the ecosystem in many ways because tree species have different, often unique properties.32. The passage mentions which of the following as effects of exotic pests on forest ecosystems? ______

单选题下面哪个方程在坐标系中表示的直线只通过一个横坐标和纵坐标都为整数的点?

单选题有7个数字：a，a，b，b，c，c，d，从中任取两个，问这两个数字相同的概率?

单选题. ①Early life insurers in the United States found themselves facing the problem of obtaining reliable information, as they needed to rely on applicants themselves to provide truthful, complete answers to a standard set of questions. ②In an attempt to personalize the relationship between insurers and their individual applicants, firms selected highly respected local citizens to act as their agents. ③These agents were expected to evaluate the appearance of candidates, unearth evidence of unhealthy family histories or questionable habits, and attest to the respectability of the people writing testimonial letters on an applicant's behalf. ④In short, the initial purpose of the agency system was not to actively solicit customers, but, rather, to recreate the glass-bowl mentality associated with small towns or city neighborhoods.3. The primary purpose of the passage is to ______

单选题有1，2，3，4，5五个数，如果偶数不能够相邻，问能够构成多少个5位数?

单选题The median of x, 15, 10 and y is 18.5. If x＜y, what’s the value of x?

单选题If two liters of a solution that is 15 percent salt will be added to 5 liters of a solution that is 8 percent salt, what percent salt will the resulting solution contain?

单选题. ①The recently announced discovery of the first known planet orbiting a pulsar (the ultradense, pulsating remnant off the supernova explosion of a star) turned out to be based on faulty data. ②Had this discovery been confirmed, theorists would have had difficulty accounting for the existence of such a planet. ③The supernova would certainly have destroyed any preexisting planets. ④This particular pulsar is relatively young, allowing little time for a new planet to have coalesced, and it rotates relatively slowly, implying that it has not interacted with any nearby star since the supernova. ①But newer evidence of a different pulsar with planets is more promising. ②This is a rapidly spurring ''millisecond pulsar" thought to be a much older object that has pulled gaseous material from a stellar neighbor, causing its rotational speed to increase. ③Leftover, unconsumed gas around such a pulsar could, in theory, coalesce into planets. ④Or the pulsar's radiation might have vaporized a companion star, providing new material for planetary formation.4. The primary purpose of the passage is to ______

单选题某一矩形的一条边是4+3S，另一条边是8-S，问矩形的周长不可能是下面哪一个?

问答题直线2y=6x+4的斜率和在x轴、y轴上的截距分别是多少?

问答题从1到100中无放回地取出两个数，两个数都为6的倍数的概率是多少?

问答题把苹果放进n个抽屉，至少放多少个苹果才能够保证至少有一个抽屉里有两个或者两个以上苹果?

问答题一批货物中12具有特征A，23具有特征B，13两种特征都具有。如果80件货物既没有特征A又没有特征B，那么一共有多少件货物?

问答题A单独完成某项工作需要x小时，B单独完成这项工作需要y小时，假设A，B两人一起工作，需要多少时间完成这项工作。

问答题从15个人中选择5个人，且有3个人不能同时选择，问有多少种选择方法?

问答题某个班一共有30个学生，其中11人参加chess club，13人参加bridge club，还有10人什么也没有参加，问有多少人仅仅参加一个club?