题目

Whether from news reports or social media articles, you may know that 5G is coming. 5G is the 5th generation network. It is a new network(网络)after 1G, 2G, 3G and 4G and it can connect everyone and everything together. 5G networks will cover/many cities in China soon. 5G means super-fast data(数据) speed, One can download a two-hour movie for fewer than 10 seconds, and it is making our hives more and more convenient. 5G will make self-driving cars possible. For safety, self-driving cars need super-fast data transmission(传输)to communicate with their nearby environment. 5G is 如图，在已知的△ABC中，按以下步骤作图：①分别以B，C为圆心，以大于 BC的长为半径作弧，两弧相交于点M、N；②作直线MN交AB于点D，连接CD，若CD=AD，∠B=20°，则下列结论中错误的是（ ）A.∠CAD=40°B.∠ACD=70°C.点D为△ABC的外心D.∠ACB=90°