Expand the expression (1-2x)².

The term independent of $x$ is the constant term.
In the expansion $1 - 4x + 4x^2$, the constant term is 1.

The term independent of $x$ is $\boxed{\text{1}}$.
Since 1 is not among options a) 15, b) -15, c) 32, d) -32, the correct option is e) None of the above.

For the expansion of $(a-b)^n$, substitute $a=1$ and $b=1$.
Sum of coefficients $= (1-1)^n = 0^n$.

If $n > 0$, then $0^n = 0$. In binomial expansion, $n$ is typically a positive integer.

The sum of the coefficients is $\boxed{\text{0}}$.
This matches option a) 0.

For $(a+b)^n$, there are $n+1$ terms. Here $n=10$, so there are $10+1=11$ terms.

Since there are 11 terms (an odd number), there is one middle term. Its position is $\frac{n+1+1}{2} = \frac{11+1}{2} = \frac{12}{2} = 6$. So, it's the 6-th term.

For the 6-th term, $k+1=6 \implies k=5$.
For $(1+x)^{10}$, $a=1$, $b=x$, $n=10$.

The question asks for "the middle term", and the options are powers of $x$. This implies we should identify the variable part of the middle term.

The middle term is $\boxed{\binom{10}{5} x^5}$. The variable part is $x^5$.
This matches option a) $x^5$.

Here, $y = -2x$ and $n = -4$.
We need the term containing $x^3$, which corresponds to the term with $y^3$.
The coefficient of $y^3$ is $\frac{n(n-1)(n-2)}{3!}$.

The term is $\frac{(-4)(-4-1)(-4-2)}{3!} (-2x)^3$.

The coefficient of $x^3$ is 160.

The coefficient of the term containing $x^3$ is $\boxed{\text{160}}$.
Since 160 is not among options a) -4, b) -8, c) 8, d) 4, the correct option is e) None of the above.

For $(1+x)^7$, $a=1$, $b=x$, $n=7$.
The term independent of $x$ is the term where the power of $x$ is 0. So, $k=0$.

The term independent of $x$ is $\boxed{\text{1}}$.
This matches option a) 1.

For $(3-2x)^5$, $a=3$, $b=-2x$, $n=5$.
We need the second term, so $k+1=2 \implies k=1$.

The coefficient of the second term is $-810$.

The coefficient of the second term is $\boxed{\text{-810}}$.
Since $-810$ is not among options a) -120, b) 240, c) -240, d) 120, the correct option is e) None of the above.

For the expansion of $(a+b)^n$, substitute $a=1$ and $b=1$.
Sum of coefficients $= (1+1)^n = 2^n$.

The sum of the coefficients is $\boxed{2^n}$.
This matches option c) $2^n$.