4. A school plans to renovate three teaching buildings during the summer vacation, and has asked three construction companies to bid on the repair costs for each building, as shown in Table 1 (unit: ten thousand yuan).
Table 1
\begin{tabular}{|l|c|c|c|}
\hline & Teaching Building 1 & Teaching Building 2 & Teaching Building 3 \\
\hline Construction Company One & 13 & 24 & 10 \\
\hline Construction Company Two & 17 & 19 & 15 \\
\hline Construction Company Three & 20 & 22 & 21 \\
\hline
\end{tabular}

Since each construction company can only renovate one teaching building during the summer vacation, the school must assign each teaching building to a different construction company. The lowest total repair cost is $(\quad)$ ten thousand yuan.
(A) 38
(B) 46
(C) 49
(D) 50
4.C.

Take three numbers from different rows and columns in the table and find their sum:
$$
\begin{array}{ll}
13+19+21=53, & 13+22+15=50, \\
17+24+21=62, & 17+22+10=49, \\
20+24+15=59, & 20+19+10=49 .
\end{array}
$$

It can be seen that the minimum total bid is 490,000 yuan.