September 18,1931 is the day that we'll never forget.为什么用that而不用when引导

September 18 ,1931 is the day____ we will never forget September 18 ,1931 is the day____ we will never forget填什么? August is b( )september Today is September first. ----is september twelfth September 18,1931 is the day that we'll never forget.为什么用that而不用when引导 T_____ Day is in September. September 10 is T( )Day September 15 is my birthday the ninth( )month is september Today is September 15 2007 对September 15 2007 提问 September ( )is teachers'day ----it is in september ( )is teachers'day ----it is in september My birthday is in September,改为疑问句. Today is September the _______(twenty) september is the______month of a year Today is the ______(two) of September