如图，在平面直角坐标系xOy中，直线y=﹣2x+a与y轴交于点C （0，6），与x轴交于点B．

    What is the strongest part of your body? Your head? Bones? It's your teeth! There is a special thing called enamel (牙釉质) in teeth. It is the hardest thing in the human body and keeps bacteria (细菌) away. However, teeth are vulnerable (易受伤害的) to problems and disease. September 20 is National Teeth-loving Day in China. Let's pay attention to the health of our teeth.
    Tooth     (1)   are    (1)   around the world. Most children and young adults have tooth decay (龋齿). A study published on China Health Monthly magazine this year showed that 40.74 percent of a sample (抽样) of 1,306 Chinese students under age 15 had decayed teeth.
(2)Food that is rich in sugar increases the risk of tooth decay. After you eat, bacteria go crazy over the sugar on your teeth, like ants at a picnic. The bacteria turn sugar into acids (酸) that eat away at tooth enamel.This cause holes in your teeth.
    Another common problem is crooked teeth (龅牙). When your new teeth begin to grow and the old teeth haven't fallen out, there isn't enough space for the new ones. This causes crooked teeth.
    Don't worry. Here are some ways to keep your teeth healthy.
    Brush at least twice a day – in the morning and before bedtime.
    Learn to use dental floss (牙线). The floss gets rid of food that's hidden where your toothbrush can't get it.
    Visit a dentist. He or she can check if you have any dental problems and help you clean your teeth.
    Pay attention to what you eat. It is better to eat lots of fruits and vegetables instead of fries and drink water instead of soda.
    Wear braces (牙套) to make your teeth straight and beautiful.

阅读下面的文言文，完成1~4题。

（一）口技

林嗣环

京中有善口技者。会宾客大宴，于厅事之东北角，施八尺屏障，口技人坐屏障中，一桌、一椅、一扇、一抚尺而已。众宾团坐。少顷，但闻屏障中抚尺一下，满坐寂然，无敢哗者。

遥闻深巷中犬吠，便有妇人惊觉欠伸，其夫呓语。既而儿醒，大啼。夫亦醒。妇抚儿乳，儿含乳啼，妇拍而呜之。又一大儿醒，絮絮不止。当是时，妇手拍儿声，口中呜声，儿含乳啼声，大儿初醒声，夫叱大儿声，一时齐发，众妙毕备。满坐宾客无不伸颈，侧目，微笑，默叹，以为妙绝。

未几，夫齁声起，妇拍儿亦渐拍渐止。微闻有鼠作作索索，盆器倾侧，妇梦中咳嗽。宾客意少舒，稍稍正坐。

忽一人大呼“火起”，夫起大呼，妇亦起大呼。两儿齐哭。俄而百千人大呼，百千儿哭，百千犬吠。中间力拉崩倒之声，火爆声，呼呼风声，百千齐作；又夹百千求救声，曳屋许许声，抢夺声，泼水声。凡所应有，无所不有。虽人有百手，手有百指，不能指其一端；人有百口，口有百舌，不能名其一处也。于是宾客无不变色离席，奋袖出臂，两股战战，几欲先走。

　　忽然抚尺一下，群响毕绝。撤屏视之，一人、一桌、一椅、一扇、一抚尺而已。

（二）卖油翁

欧阳修

陈康肃公尧咨善射，当世无双，公亦以此自矜。尝射于家圃，有卖油翁释担而立，睨之，久而不去。见其发矢十中八九，但微颔之。康肃问曰：“汝亦知射乎？吾射不亦精乎？”翁曰：“无他，但手熟尔。”康肃忿然曰：“尔安敢轻吾射！”翁曰：“以我酌油知之。”乃取一葫芦置于地，以钱覆其口，徐以杓酌油沥之，自钱孔入，而钱不湿。因曰：“我亦无他，惟手熟尔。”康肃笑而遣之。