Would you check the correctness of 25 sentences?

[vil]

Dear teachers,

Would you be kind enough to check the correctness of the following sentences?

1.He told my old man she wasn’t going to let Handsome and me break our backs picking berries.
2.I am not going to do anything behind his back. If necessary I’ll tell him about it straight to his face.
3.It is the last straw that broke the camel’s back.
4.They turned their backs on him when he most needed them.
5.I never thought that he was capable of stabbing anybody in the back.
6.The cat arched its back.
7.The heavy bag was on his back.
8.They stood with their backs to the door.
9.They were put in a room at the back of the house.
10.We sat at the back of the car.
11.There is a garden at the back of the house.
12.I thought that in the back of my mind.
13.He did it behind my back.
14.Please, get off my back!
15.How do you get back my girlfriend?
16.If you scratch my back, I’ll scratch yours.
17.I have my back to the wall.
18.I’ll put my back into the work in question.
19.Who will sit in back?
20.The independents will back us against the majority party.
21.I will back her for public office.
22.You have to back into a garage.
23.She backed the car into the driveway.
24.He backed out of the driveway.
25.They backed out of the deal.

Thank you for your efforts.

Regards,

V.

[MrPedantic]

Hello Vil,

All looks good, except:

3. You have combined two idioms!
10. "at the back of the car" - a different preposition would be more idiomatic.
12. "At the back of my mind" tends to appear at the beginning of the clause or sentence; it then tends to be followed by a quite long explanation.
15. The context here is difficult to imagine.
19. Cf. some of your other examples...

All the best,

MrP

[Monticello]

xxx
Hi vil,

All are OK except for these three:

3.It is the last straw that broke the camel’s back.

Note: "The last straw" and "The straw that broke the camel's back" though related, are two separate idioms. Don't mix them; use one or the other: a) It's (or That's) the last straw! (- meaning the straw that breaks the camel's back); b) That's the straw that broke the camel's back.

10.We sat at the back of the car.

In the US, one would say "in the back of the car" or "in the back seat." Being American, I'm not sure if "at the back of the car" is acceptable UK usage.

15.How do you get back my girlfriend?

The problem here is the mix of second person -- you -- and first person -- my. Why not: How does one (or do you) get a lost love (or a girlfriend) back? - or better: Can one ever get a lost love back? Please note that "get back a lost love," though acceptable, does not work as well here as "get a lost love back."