The correct answer is $\boxed{\text{B) 43}}$.
To convert a binary number to decimal, you multiply each digit by 2 raised to the power of its position, starting from the right. The position of the rightmost digit is 0, the next digit is 1, and so on.
In the binary number $101101_2$, the digits are in the positions $2^4$, $2^3$, $2^2$, $2^1$, and $2^0$. The
corresponding values are $16$, $8$, $4$, $2$, and $1$. Multiplying each digit by its value and adding the products gives:$$101101_2 = (1 \cdot 16) + (0 \cdot 8) + (1 \cdot 4) + (1 \cdot 2) + (1 \cdot 1) = 43_{10}$$
Option A is incorrect because $45_{10}$ is not equal to $101101_2$. Option C is incorrect because $40_{10}$ is not equal to $101101_2$. Option D is incorrect because $47_{10}$ is not equal to $101101_2$. Option E is incorrect because there is a correct answer.