It’s difficult for me____ an English letter.[ ]

Kitty, there’s ________ cooking oil left in the kitchen. Would you please go to the supermarket and get ________?— OK, Mum.

It’s difficult _____ your sound because the noise is too high.

His father served in the army in ________ when he was in ________.

I have ________ useful knife and my sister has _______ eraser.