Is the following an expression or a sentence?
$2 + 2$
A. Expression
B. Sentence

Is the following an expression or a sentence?
$2 + 2 = 4$
A. Expression
B. Sentence

Is the following an expression or a sentence?
$2 + x$
A. Expression
B. Sentence

Is the following an expression or a sentence?
$S \cap T$
A. Expression
B. Sentence

Is the following an expression or a sentence?
$S \subset T$
A. Expression
B. Sentence