card|cards

妈妈给我寄了一张生日贺卡。

My mom sent me a birthday ___card in the mail.

明天是我朋友的生日，所以我必须给她寄张贺卡。

It's my friend's birthday tomorrow, so I must send her a ___card.

做一些卡片吧。

Make some ___cards.