when is your parents birthday?这里is 为啥不变are

when is your birthday?how are you? When is your birthday? when is your birthday回答 WHEN IS YOUR BIRTHDAY?(回答) When is your u__ birthday? When is your birthday on? When is your birthday?英文翻译 Are you happy when your birthday is coming? when is your birthday为什么用are提问 when ＿＿ （is,are ）your birthday when is your birthday?it is( ) when is your birthday?my birthday is on _.