Which of the following sentences is a statement ?

Question

$\begin {array} {1 1} (A)\;Mathematics\: is\: difficult \\ (B)\;The\: sum\: of\: 5 \:and \:  7\:is \: greater \: than \: 10 \\ (C)\;The\: square\: of \: a \: number \: is \: an \: even\: number. \\ (D)\;Answer \: this\: question. \end {array}$