you have to stay at home because it______(rain)heavily outside

you have to stay at home because it______(rain)heavily outside
为什么不用现在完成时,一般现在时?
2Here___ Sandy.Her pink scarf___ her silk blouse well.为什么不用is coming,这不也是表将来吗
3.it tried hard to do whatever it ____to stay on the leaf.
请帮我分析一下第三个句子