7. In the arithmetic sequence $13,16,19, \cdots, 70,73$, there are ( ) terms.
(A) 20
(B) 21
(C) 24
(D) 60
$(\mathrm{E}) 61$
7. B.

Notice that the first term of the arithmetic sequence is 13, the common difference is 3, and the last term is 73. Therefore, the number of terms is $\frac{73-13}{3}+1=21$.