To find the number of terms in the arithmetic sequence where the first term \( U_1 = 2 \), the common difference \( d = 4 \), and the last term is \( U_n = 90 \), use the formula for the \( n \)-th term of an arithmetic sequence:

\[
U_n = U_1 + (n - 1) \times d
\]

Step-by-Step Solution:

1. Substitute the given values into the formula:

\[
90 = 2 + (n - 1) \times 4
\]

2. Solve for \( n \):

\[
90 - 2 = (n - 1) \times 4
\]
\[
88 = (n - 1) \times 4
\]
\[
n - 1 = \frac{88}{4} = 22
\]
\[
n = 22 + 1 = 23
\]


The number of terms in the sequence is 23.

The correct answer is D. 23.