4. In modern society, the difficulty of deciphering passwords is increasing. There is a type of password that breaks down English plaintext (real text) into letters, where the 26 English letters $\mathrm{a}, \mathrm{b}, \cdots, \mathrm{z}$ (regardless of case) correspond to the 26 natural numbers $1,2, \cdots, 26$, as shown in Table 1.
Table 1
\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|c|c|c|}
\hline a & b & c & d & e & f & g & h & i & j & k & l & m \\
\hline 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & 11 & 12 & 13 \\
\hline n & o & p & q & r & s & t & u & v & w & x & y & z \\
\hline 14 & 15 & 16 & 17 & 18 & 19 & 20 & 21 & 22 & 23 & 24 & 25 & 26 \\
\hline
\end{tabular}

A transformation formula is given as follows:
$$
x^{\prime}=\left\{\begin{array}{l}
\frac{x+1}{2}, \text{ if } x \text{ is odd and } 1 \leqslant x \leqslant 26 ; \\
\frac{x}{2}+13, \text{ if } x \text{ is even and } 1 \leqslant x \leqslant 26 .
\end{array}\right.
$$

Using this formula, plaintext can be converted into ciphertext. For example, $8 \rightarrow \frac{8}{2}+13=17$, which means $h$ becomes $\mathrm{q} ; 5 \rightarrow \frac{5+1}{2}=3$, which means $\mathrm{e}$ becomes $\mathrm{c}$.

According to the above formula, if the ciphertext obtained from a certain plaintext is shxc, then the original plaintext is ( ).
(A) Ihho
(B) ohhl
(C) love
(D) eovl
4.C.

The inverse transformation formula is
$$
x=\left\{\begin{array}{ll}
2 x^{\prime}-1, & 1 \leqslant x^{\prime} \leqslant 13, x^{\prime} \in \mathbf{N} ; \\
2 x^{\prime}-26, & 14 \leqslant x^{\prime} \leqslant 26, x^{\prime} \in \mathbf{N} .
\end{array}\right.
$$

According to the above transformation, we have
$$
\begin{array}{l}
\mathrm{s} \rightarrow 19 \rightarrow 2 \times 19-26=12 \rightarrow \mathrm{l}, \\
\mathrm{h} \rightarrow 8 \rightarrow 2 \times 8-1=15 \rightarrow \mathrm{o}, \\
\mathrm{x} \rightarrow 24 \rightarrow 2 \times 24-26=22 \rightarrow \mathrm{v}, \\
\mathrm{c} \rightarrow 3 \rightarrow 2 \times 3-1=5 \rightarrow \mathrm{e} .
\end{array}
$$

Therefore, the plaintext of shxc is love.