A:Sorry, he is busy at the moment.
B:Why didn't you call earlier?
C:Certainly. May I know your name?
D:Sorry, he doesn't want to see you.
元旦晚会上,九年级(1)班43名同学和7名老师每人写了一张同种型号的新年贺卡,放进一个纸箱里充分摇匀后,小红从纸箱里任意摸出一张贺卡,恰好是老师写的贺卡的概率是____.
请你用化学符号填空: