Answer
a) More resistive.
b) Quickly.
c) Decreased.
Work Step by Step
We know that in a damped system, the energy decays exponentially and is given by
$$E=E_0e^{\frac{-t}{\tau}}$$
where $\tau$ is the time constant and is given by $$\tau=\dfrac{m}{b}$$
Now the author told us that the damping constant $b$ increases which mean that the time constant decreases.
The decrease of time constant $\tau$ increases the term of $e^{-t/\tau}$ and this means that energy will be removed from the system faster.
From all the above;
a) The medium is more resistive since $b$ increases.
b) And the oscillations damp out more quickly.
c) As mentioned above, the time constant $\tau$ decreases.
