选择正确的情态动词
I really think you________(should/could) visit the Three Gorges Dam. It's really fascinating.
I ________(had to/should) show the captain my travel documents when I arrived.
I'm afraid I ________(couldn't/can't) stay more than three days. I ________(have to/can) return to work next Monday.
It ________(will/can be) a great trip because there are so many interesting things to see.
We ________(can't/couldn't) see the mountain peaks because it rained heavily every day.
There ________(won't/can't) be many people on the boat because It's a trading ship.