如果表示他去了没去的状态,用过去时.例如：
It is Sunday today,I saw he went to picnic in the morning.今天是星期天,我看见他去野炊.
如果表示他今天的计划干什么,用一般现在时,或现在进行时.例如
It is Suday today,he goes for a picnic as the plan.
It is Sunday today,he is going for a picnic as the plan
今天是星期天,按照计划他要去野炊.