题目详情:

[单项选择]患者，男，10岁，替牙期。因自觉上牙前突前来就诊。患者侧面为凸面型，下颌明显后缩，磨牙关系为远中尖对尖，前牙覆盖7mm，上前牙明显唇倾拟对患者进行双期矫治，第一期使用TwinBlock矫治器改善上下颌骨矢状向不调。关于TwinBlock矫治器的组成，下列说法不正确的是（）。
A. 内收上前牙的唇弓
B. 下颌前磨牙的改良箭头卡环或三角形箭头卡环（Delta卡环）
C. 上颌磨牙的改良箭头卡环或三角形箭头卡环（Delta卡环）
D. 垫
E. 下前牙的唇弓

热门试题:

[单项选择]空心圆杆受轴向拉伸时，受力在弹性范围内，外径与壁厚的变形关系有四种：（）
A. 外径和壁厚都增大
B. 外径和壁厚都减小
C. 外径减小，壁厚增大
D. 外径增大，壁厚减小

[不定项选择题]共用题干 Saving a City's Public Art
Avoiding traffic jams in Los Angeles may be impossible,but the city's colorful freeway mu-rals（壁画）can brighten even the most miserable commute. Paintings that depict（描述）famous people and historic scenes cover office buildings and freeway walls across the city.With a collec- tion of more than 2,000 murals,Los Angeles is the unofficial mural capital of the world.
But the combination of graffiti（涂鸦）,pollution,and hot sun has left many L. A. murals in terrible condition.______(46)In the past,experts say,little attention was given to caring for public art. Artists were even expected to maintain their own works,not an easy task with cars rac-ing by along the freeway.______(47)The work started in 2003 .So far,16 walls have been Se-lected,and more may be added later.
Until about 1960,public murals in Los Angeles were rare.But in the 1960s and 1970s, young L. A. artists began to study early 20th-century Mexican mural painting.______(48)
The most famous mural in the city is Judith Baca's“The Great Wall,”a 13-foot-high(4-me-ter-high)painting that runs for half a mile(0 .8 kilometer)in North Hollywood.______(49)It took eight years to complete-400 underprivileged teenagers painted the designs-and is probably the longest mural in the world.
One of the murals that will be restored now is Kent Twitchell's“Seventh Street Altarpiece.” which he painted for the Los Angeles Olympics in 1984.______(50)Twitchell said,“It was meant as a kind of gateway through which the traveler to L. A.must drive.The open hands repre- sent peace.”
Artists often call murals the people's art. Along a busy freeway or hidden in a quiet neighbor-hood,murals can teach people who would never pay money to see fine art in a museum,“Murals give a voice to the silent majority,”said one artist. ______(47) A:The city,trying to stop the spread of graffiti,has painted over some of the murals com- pletely.
A.This striking work depicts two people facing each other on opposite sides of the freeway near downtown Los Angeles.
B.Artists like murals because they like the work of Mexican artists.
C.Now the city is beginning a huge project to restore the city's murals.
D.The mural represents the history of ethnic groups in California.
E.Soon,their murals became a symbol of the city's cultural expressions and a showcase for L.
F.'s cultural diversity.