Is this と (particle) + したら or is it "としたら"

Question

It's an exercise from my textbook where I have to fill in a word from a list. The list is: なる, 渡る, 話す, できる, たいへんな, 降りる.

The sentence in question is as follows:

電車を _______ としたら、ドアが閉まってしまった。

I don't think that と+したら could make any sense here, but my textbook hasn't taught me the word としたら http://jisho.org/search/toshitara yet so I can't rule it out. That's why I'm asking you what you think.

I would insert 降りる here and translate the sentence as follows: "If it happens that I exit the train, unfortunately the door will close."

Answer 1

降りる is obviously the verb you want, but I think the exercise must expect you to put it into the tentative form, 降りよう. 降りようとしたら, "When I made to get off", "Just as I was going to get off", would make sense here. I expect you know the rule:

Tentative form + とする = make as if to do, be about to do, be going to do, be on the point of doing, try [unsuccessfully] to do.

For example:

• お風呂に入ろうとすると, "just as I was about to get into the bath [the telephone rang]"
• 10時になろうとしています "[Radio announcer] It's just coming up to ten o'clock"
• 窓を開けようとしたが "I tried to open the window [but it was jammed]".

So your completed sentence would mean "Just as I was going to get off the train, the door closed" (or maybe "the damned door" to convey the irritation expressed by しまった)

Answer 2

電車を「降りよう」としたら、ドアが閉まってしまった。

When I was getting off the train, unfortunately the door closed.
Literally, when I tried to get off the train, unforfunately the door closed.

降りる must be properly conjugated to 降りよう.