The word "Mistake" is wrong.

A river.

81
(a+b=c, b+c=d, c+d=e …)

"143"
Represents the number of letters in each word of the phrase.

10

2n + 2 = 22 => 2n = 20 => n = 20 / 2 => n = 10

You can say any sentence with a true fact, but the subject of the fact must be vaguely named. For example: “A scientist discovered that things were able to fall to another object due to gravity.” In this sentence, it’s obviously about how Isaac Newton discovered gravity, BUT his name wasn’t ‘A scientist.’ Sure, it’s a grey area, but it still works.

The two babies are two of a set of triplets.

A. FALSE, B. TRUE, C. TRUE, D. FALSE
Canberra is the capital of Australia; Gauguin was a French post-impressionist painter.

Darkness

The morning dew.

All apples grow on trees.

Pepper.