will构成一般将来时 — 英语填空题
题目
周末，Tom 写下了他的计划：
1. He ___ (visit) his grandparents on Saturday morning.
2. They ___ (have) a picnic in the park on Sunday.
3. It will rain tomorrow, so they ___ (not swim) in the river.
（用 will 或 will not 加括号中动词原形补全句子）