The table shows the frequency distribution of the number of chairs in each of the 40 rooms of various houses. Use the information to answer questions 5 to 7.

$1 \times 2 = 2$
$2 \times 7 = 14$
$3 \times 5 = 15$
$4 \times 4 = 16$
$5 \times 9 = 45$
$6 \times 7 = 42$
$7 \times 6 = 42$

The mean is $\boxed{\text{C. 4.4}}$.

The frequencies are 2, 7, 5, 4, 9, 7, 6.
The highest frequency is 9.

The number of chairs corresponding to the frequency 9 is 5.

The mode is $\boxed{\text{D. 5}}$.

$N = \sum f = 40$.

Since $N$ is an even number, the median is the average of the $\left(\frac{N}{2}\right)$-th and $\left(\frac{N}{2} + 1\right)$-th values.
$\frac{N}{2} = \frac{40}{2} = 20$.
So, we need the 20th and 21st values.

From the cumulative frequency table:
The 1st to 2nd values are 1.
The 3rd to 9th values are 2.
The 10th to 14th values are 3.
The 15th to 18th values are 4.
The 19th to 27th values are 5.
Therefore, both the 20th value and the 21st value are 5.

The median is $\boxed{\mathbf{5}}$. (Note: The visible options A. 6.5 and B. 9.0 do not include 5.0, which is the calculated median.)