小明足部受伤发炎，医生在其左臂静脉滴注抗生素，药物到达足部的途径是（ ）
①左心房；②右心房；③右心室；④主动脉；⑤肺动脉；⑥肺静脉；⑦上腔静脉；⑧下腔静脉；⑨股动脉；⑩左心室．
A：①③④⑥②⑦⑧⑨⑩
B：⑦②③⑤⑥①⑩④⑨
C：⑦②③⑤⑥①⑧④⑨
D：⑦②③⑥⑤①⑩④⑨
Many students take the school bus to school every day. Parents think taking the school bus is usually safe (安全的), but sometimes it is dangerous. Some students don't keep the school bus rules. What are the school bus rules?
Arrive at the bus station early.
Wait for (等候) the school bus at the bus station.
Don't run at the bus station.
Don't walk or fight on the bus.
Don't get off (下车) the bus when it goes.
判断对错.
如果a:b=3:5，那么a一定是3，b一定是5.
