用所给单词的适当形式填空。 1. You can’t get out of your seat during the ______ (fly), because it’s dangerous. 2. When that plane took off, this one has already landed in the a
Life has changed in Mexico City．Streets normally filled with people are empty．One of the most popular professional soccer teams recently played a game in an empty stadium that can seat more than10
过焦 点F的弦与抛物线交于A、B两点，过A、B分别作y轴垂线，垂足分别为C、D，则|AB|+|BD|的最小值是 。