One
They were looking on a beetle in the grass.
They were looking at a beetle in the grass.
It is raining when I got home last night.
It was raining when I got home last night.
I have not ate anything today.
I have not eaten anything today.
My father is thinking that I should stop smoking.
My father thinks that I should stop smoking.
I have lived in Canada since 10 months.
I have lived in Canada for 10 months.
If the world ended tomorrow, I will be very sad.
If the world ended tomorrow, I would be very sad.
The students were not interested in the lesson because it was bored.
The students were not interested in the lesson because it was boring.
If I will be late, I'll call you.
If I am late, I'll call you.
Explanation: This is the first conditional (Future Real).
I need to concentrate myself on my homework.
I need to concentrate on my homework.
Explanation: You cannot use a reflexive pronoun after concentrate.
Most adults are taller than most children.
Most adults are taller than most child.
This was the most excited story I have ever read.
This was the most exciting story I have ever read.
She felt everyone looked boring with the story she was telling.
She felt everyone looked bored with the story she was telling.
We can't play tennis anymore because it rains.
We can't play tennis anymore because itis raining.
I often do mistakes when I speak Spanish.
I often make mistakes when I speak Spanish.
Explanation: make is an act of creation. There was no mistake until you created it (made it).
People have been waiting in line for 2 hours even though it have been raining the whole time.
People have been waiting in line for 2 hours even though it has been raining the whole time.