题干

某校的研究性学习小组开展了“探究洋葱根尖分生组织细胞有丝分裂的日周期性”的课题研究,以确定洋葱根尖取材的最佳时间.细胞分裂指数是衡量洋葱根尖细胞分裂状况的指标之一,分裂指数=
×100%.实验操作步骤如下:

第一步:取多个已经培养好的洋葱鳞茎(根长约为5cm)作为实验材料.

第二步:在某一天的8~18点时间段内每隔1小时,取3根洋葱根尖分别制成临时装片.

制作临时装片的方法如下:

①解离:剪取洋葱根尖2~3mm,立即放入盛有质量分数为15%的盐酸和体积分数为95%的酒精混合液(体积比为1:1)的玻璃皿中,在室温下解离15min.

②染色:把根尖放进盛有质量浓度为0.01g/mL 龙胆紫溶液的玻璃皿中染色3~5min.

③漂洗:将根尖放入盛有清水的玻璃皿中漂洗约 10min.

④制片:将根尖放在载玻片上,加一滴清水,并用镊子把根尖弄碎,盖上载玻片后,再加一片载玻片,用拇指轻轻按压载玻片.

第三步:观察、计数并将结果记录在表格中.

请回答下列问题:

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阅读理解

    Denali National Park, Alaska

    History

    Within Denali National Park, the Toklat River will always have a special significance, as it was the location where naturalist Charles Sheldon built a cabin and was so moved that he fought to preserve the land. He moved back east and spent nine years lobbying (游说)to create Alaska's first national park.

    When to Visit

    To avoid the crowds, visit in June, but keep in mind that there are up to 21 hours of sunlight in Alaska in summer. If it seems like a bit much for your taste, try visiting in late August or September.

    If you visit to climb Mount McKinley, May and early June are the best times to climb.

    Major Attractions

    It is difficult not to see Denali's largest attraction towering 20,320 feet high. Mount McKinley can even be seen up to 70 miles away on a clear day. If you brave the climb to the top, you will be rewarded with charming views of the Alaska Range.

    Sable Pass is a prime spot to view grizzly bears. Closed to off-road foot traffic, the area is popular for bears feeding on berries, roots, and even occasionally on other mammals.

    Beginning at just below the summit of Mount McKinley, Muldrow Glacier flows 35 miles through a gorge and across the tundra. Twice in the last hundred years, the Muldrow has surged (涌动), most recently in the winter of 1956-1957.

Accommodation

    Five campgrounds are located within the park, and many are open from late spring to early fall.Note: reservations are strongly recommended during summer. Riley Creek campground is open all year round, and all but two (Sanctuary and Wonder Lake) offer RV (可供居住的大篷车)sites.

    Also within the park are a few lodges (旅馆)—North Face Lodge, Denali Backcountry Lodge and Kentishna Roadhouse.

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如图,正方形网格中,已有两个小正方形被涂黑,再涂黑另外一个小正方形,使整个被涂黑的图案构成一个轴对称图形的方法有(  )

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The____(安全) is the first.

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综合题。

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我国自行研制的长征系列火箭,在世界上处于领先水平。如图所示,长征系列火箭的起飞推力为3×106N,请在图中画出火箭上升过程中受到推力的示意图。

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