题干

下列哪一结构不是所有细胞共有的

A:细胞膜

B:细胞质

C:线粒体

D:核糖体

上一题 下一题 0.0难度 选择题 更新时间:2017-10-15 04:02:30

答案(点此获取答案解析)

C

同类题4

阅读下面选文,回答下列各题。

    【甲】一屠晚归,担中肉尽,只有剩骨。途中两狼,缀行甚远。

    屠惧,投以骨。一狼得骨止,一狼仍从。复投之,后狼止而前狼又至。骨已尽矣,而两狼之并驱如故。

    屠大窘,恐前后受其敌。顾野有麦场,场主积薪其中,苫蔽成丘。屠乃奔倚其下,弛担持刀。狼不敢前,眈眈相向。

    少时,一狼径去,其一犬坐于前。久之,目似瞑,意暇甚。屠暴起,以刀劈狼首,又数刀毙之。方欲行,转视积薪后,一狼洞其中,意将隧入以攻其后也。身已半入,止露尻尾。屠自后断其股,亦毙之。乃悟前狼假寐,盖以诱敌。

    狼亦黠矣,而顷刻两毙,禽兽之变诈几何哉?止增笑耳。

    【乙】两牧竖①入山至狼穴,穴有小狼二,谋分捉之。各登一树,相去②数十步。少顷,大狼至,入穴失子,意甚仓皇。竖于树上扭小狼蹄耳故令嗥,大狼闻声仰视,怒奔树下,号且爬抓。其一竖又在彼树致鸣急;狼闻四顾,始望见之,乃舍此趋彼,跑③号如前状。前树又鸣,又转奔之。口无停声,足无停趾,数十往复,奔渐迟,声渐弱,既而奄奄④僵卧,久之有动。竖下视之,气已绝矣。

【注释】①牧竖:牧童。竖,童仆。②去:距离③跑:同“刨”用足趴地。④奄奄:气息微弱的样子。

同类题5

任务型阅读

    Youth sport has the potential to accomplish three important objectives in children's development. First, sport programs can provide youth with opportunities to be physically active, which can lead to improved physical health. Second, youth sport programs have long been considered important to youth's psychosocial development, providing opportunities to learn important life skills such as cooperation, discipline, leadership, and self-control. Third, youth sport programs are critical for the learning of motor skills; these motor skills serve as a foundation for future national sport stars and recreational adult sport participants. When coachers develop activities for youth practices and when sport organizations design youth-sport programs, they must consider the implication of deliberate play and deliberate practice.

Research from Telama (2006) states that regular participation in deliberate play or deliberate practice activities during childhood and youth (ages nine to eighteen) increases the likelihood of participation in sports during adulthood by six times for both males and females. Côté (2002) defines deliberate play activities in sport as those designed to maximize enjoyment. These activities are regulated by flexible rules adapted from standardized sport rules and are set up by the children or by an involved adult. Children typically change rules to find a point where their game is similar to the actual sport but still allows for play at their level. For example, children may change soccer and basketball rules to suit their needs and environment (e.g. in the street. on a playing field or in someone's backyard). When involved in deliberate play activities, children are less concerned with the outcome of their outcome of their behavior. (whether they win or lose) than with the behavior. (having fun).

    On the other hand, Ericsson (1993) suggests that the most effective learning occurs through involvement in highly structured activities defined as deliberate practice. Deliberate practice activities require effort, produce no immediate rewards, and are motivated by the goal of improving performance rather than the goal of enjoyment. When individuals are involved in deliberate play, they experiment with different combinations of behaviors, but not necessarily in the most effective way to improve performance. In contrast, when individuals are involved in deliberate practice, they exhibit behavior. focused on improving performance by the most effective means available. For example, the backhand skills in tennis could be learned and improved over time by playing matches or by creating fun practice situations. However, players could more effectively improve their backhand performance by practicing drills that might be considered less enjoyable. Although drills are used in most effective means available practice might not be the most enjoyable, they might be the most relevant to improving performance.

    (Note: Answer the questions or complete the statements in NO MORE THAN TEN WORDS)