Making an expression with 'i presume'

A school teacher asked her class to make a sentence containing the expression “I presume”.
One little girl held up her hand and said: “Yesterday my mother hand washed the dinner dishes so I presume the dishwasher was broken.”
“Very good” said the teacher.
Another one said: “This morning, my father drove the Volkswagen out of the garage. I presume the BMW wouldn’t start.”
“That’s excellent” says the teacher.
Little Johnny at the back of the classroom gets up and says: “Yesterday I saw grandpa leave the house with a newspaper under his arm and he headed for
the bush, I presume that....”
The teacher interrupted him and said, “I stopped you because you have no idea what your grandfather was going to do, so you can’t presume anything.”
Johnny says, “Please Teacher, let me finish my sentence.”
The teacher says, “Very well. Continue.”
“As I was saying, I saw my grandpa heading for the bush with a newspaper under his arm. I presume he was going for a shit because he can’t read.