Answer
a. A has a greater resistance than B at voltage $V_{1}.$
b. Explanation II is best.
Work Step by Step
$a.$
At voltage $V_{1}$, material B allows more current to pass than material A, so A has a greater resistance than B at voltage $V_{1}.$
$b.$
Both graphs show current $(I)$ as a function of voltage $(V). $
The red graph is linear, $I=mV.$
To find the slope m, we use Ohm's Law and solve for $I.$ We assume that both materials adhere to the law.
$I=(\displaystyle \frac{1}{R})V$
We interpret this as the slope being the reciprocal value of R.
The higher the slope, the lower R is.
In the case of material A, slope is constant, so R is constant regardless of V.
In the case of B, slope increases as V grows, and, the greater the slope, the LOWER the resistance of B.
Thus, explanation II is the best (III is wrong and I is correct, but lacking in information).
