congratulation作不可数时意为“祝贺”,用于一般句中,例如：
He gave a speech of congratulation for the winner.
He gave sincere congratulation to him.
congratulation作可数时只用复数形式,即congratulations,表示“向某人祝贺”时用congratulations to sb. 表示“因……祝贺某人”时用congratulations sb. on sth.。如：
Congratulations to you! 祝贺你!
Congratulations to you on your success! 祝贺你获得成功!
