题干

密度知识与生活联系非常紧密,下列关于密度的一些说法中正确的是(    )

A:1kg冰与1kg水的密度相等

B:乒乓球不慎被挤瘪但无破损,球内气体密度变大

C:为减轻质量,比赛用自行车采用强度高、密度大的材料制造

D:节日放飞的气球可以飘在空中,是因为气球内部气体的密度比空气大

上一题 下一题 0.0难度 选择题 更新时间:2019-01-15 09:31:21

答案(点此获取答案解析)

B

同类题4

阅读理解

    “Smombies” are very real and a growing cause for concern. Tired of having to constantly warn both locals and tourists to pay more attention to their surroundings to avoid serious accidents, authorities of a small German town have come up with a more positive solution — embedding (嵌入) traffic lights in the pavement to make them visible to people constantly looking down at their phones while walking.

    The seemingly ridiculous safety measure was put in place. Authorities in Augsburg decided to act, installing ground level traffic lights at two tram (有轨电车) stops last Tuesday. The lights flash red every time a tram is approaching, or when the regular traffic light turns red. “We realized that the normal traffic light isn't in the line of sight of many pedestrians these days,” said Tobias Hermes, a city administration official. “So we decided to have an additional set of lights — the more we have, the more people are likely to notice them.”

    Some Augsburg residents appear to be quite happy with the idea. “I think it makes sense,” said Jack Smith, “One always sees young people these days running over red lights. This makes it more obvious that you need to stop.” Others, however, found the need for ground traffic lights disturbing and even frightening. “I find it scary that smart phone users are so engrossed that they need to install lights in the ground so that they notice the tram coming,” one person told the local paper.

    But do this kind of pavement-embedded lights actually work? Well, if one interviewed teenager is to be believed, not really, “To be honest I didn't even notice it,” he said, “Maybe it'd be useful at night, but yeah, I didn't realize it was there until just now.”

    The word “smombie” — a mashup of the words smart phone and zombie — was born in Germany. It was voted “youth word of the year” in 2017, but the serious consequences of this behaviour are no laughing matter.