Sentences

[ZeRinku]

Well I have more sentences that I need help with but its only 4 sentences this time.

First I said

私の車はどうして彼を任せりました？

Then I was corrected to this

私の車をどうして彼に任せたのですか？

What I was trying to say was "Why did I entrust my car to him?" so I am not understanding the corrections. Also I see that 任せりました in the first sentence was corrected to the casual past 任せた in the correction. So my question about that is の comes after 任せた and then ですか and I know that です is added at the end of a sentence without a verb to make the sentence polite...so the の after 任せた allows you to use です after it?

EDIT: I just realized I conjugated 任せる wrong it should be 任せました does that have any effect on why she corrected it the way she did?

Next one

天はきっときれいだろう。

Corrected to

空はきっときれいだろう。

When she was correcting this sentence she thought I meant sky so she replaced 天 with 空. I was trying to say "Heaven is surely pretty". I know that 天 can mean sky also but I was trying to say heaven so was my sentence right and she just thought I meant sky? Or no?

Next one

誰に来た？

Corrected to

誰か来た？

I was trying to say "Who came?" but I'm pretty sure the corrected sentence means "Someone came?". I'm not sure what I did wrong...

Last one

任天堂はすごいだぞ！

Corrected to

任天堂はすごいぞ！

I think I know what I did wrong here but I just want to make sure. I used the declarative だ with an i-adjective and you can't do that. Thats what I did wrong, right?

[Psy]

I've gotta run so I'll be brief:

私の車はどうして彼を任せりました？
Then I was corrected to this
私の車をどうして彼に任せたのですか？

You corrected yourself with the conjugation, as this is an いる／える verb. The second part, with the の (often shortened to just ん), is often explained as carrying an explanatory tone, but in this case it's best to think of it as asking further information about a situation that is already clear to both people. In general one doesn't speak to oneself in polite form, though.

天はきっときれいだろう。
Corrected to
空はきっときれいだろう。

There's some overlap between sky and heaven in the character 天, so to clarify what you meant you should say 天国.

誰に来た？
Corrected to
誰か来た？
I was trying to say "Who came?" but I'm pretty sure the corrected sentence means "Someone came?". I'm not sure what I did wrong...

You're right about the correction meaning "someone came." Since you're wanting ask "who came?" Remember that "who" is the subject and thereby takes が. は is never used in such situations. Thus, you should ask 誰が来た?

任天堂はすごいだぞ！
Corrected to
任天堂はすごいぞ！
I think I know what I did wrong here but I just want to make sure. I used the declarative だ with an i-adjective and you can't do that. Thats what I did wrong, right

Yup. Common mistake. I hear it even from higher-level students sometimes, or at least students pretending to be high-level. Nip it in the bud now before it becomes a habit. Great job on catching it.

[ZeRinku]

Thank you, Psy!

[QuackingShoe]

More importantly, your sentence as written (ignoring conjugation errors) is asking why your car entrusted him to someone else, instead of why someone entrusted your car to him. You marked 'him' with the direct object particle. You need to mark him with に instead, and the car with を, because the car is what you're entrusting and 彼 is who you're entrusting to.

[jkeyz15]

車 can be marked with は or を. As for which it all depends on the nuances, but I would say you should go with を here.