A:它们的运动方向相同
B:它们的运动方向相反
C:在t1时刻甲的速度比乙的速度大
D:在t2时刻二者相遇
根据短文内容,用方框中所给词的适当形式填空。
but, favorite, want, about, hamburger, and, like, often, I, visit
Dear Han Mei,
Thank you for your letter. I ____ China very much. And I ____ to go to China with my parents. We want ____ Beijing. I know something ____ China from your letters. ____. I don't know much about Chinese food. Could you tell ____ something about it?I like ____ and fish very much. You tell me you ____ eat rice, vegetables and chicken. And your ____ food is jioazi. What kind of food ____ drink can I have in China? Please tell me.
生物的亲子间和子代个体间的相似性叫做____;亲子间或子代个体间的差异叫做____.这两种现象是生物界普遍存在的现象,它们是通过____和____而实现的.
(Ⅰ)若⊙F被l所截得的弦长为 25 ,求|AB|;
(Ⅱ)判断直线PA与C的交点个数,并说明理由.
酪氨酸酶存在于正常人的皮肤和毛囊等处的细胞中,它能促使酪氨酸转变为黑色素,若编码此酶的基因发生了突变将导致白化病,这种现象说明( )