it's hard to navigate.为什么要用to?如果要用的话后面动词怎么不加ing?对不起,越学越糊了.这里to是介词吗?为什么要用to?如果是介词,后面的动词为什么变成动名词形式?

it's hard to it's hard to tell~ “It's hard to die. It's hard to comments to me. it's hard to make living It's hard to die怎么解释? It's hard to study English. 有没有It's hard to me it's very hard to p___everyone It's hard to say意思 but It's hard to 如题 it's so hard to say It's hard to tell!3Q It's hard to grow wheat. it's hard to find that kind It's hard to be a man. but it's hard to leave是什么意思 it's hard to join the fray