①上腔静脉②左心房③右心房④左心室⑤右心室⑥肺动脉⑦肺静脉
A:①②③④
B:①③⑤⑥
C:①②⑤⑥
D:①③⑤⑦
如图,设A、B、C、D为4个居民小区,现要在四边形ABCD内建一个购物中心,试问应把购物中心建在何处,才能使4个居民小区到购物中心的距离之和最小?说明理由.
When I got to the bus stop. I missed the early bus and I had to____ the next one.