I had lunch. 这是一个简单的过去动作. 没有特别意义就是你吃过了,通常在日记里写的没意义的过去完成的事.i've already had lunch. have had lunch, 是你告诉人你已经吃过了, 和现在有关联的. 如果有人约你去吃饭,你...