Can someone please help explain this (or provide a website link). I know the answer is (a).
To decide whether or not the slope coefficient is large or small,
a) you should analyze the economic importance of a given increase in X.
b) the slope coefficient must be larger than one.
c) the slope coefficient must be statistically significant.
d) you should change the scale of the X variable if the coefficient appears to be too small.
You should always do a) and c). However it won't help you "decide whether or not the slope coefficient is large or small", because being large or small is not meaningful. A coefficient can be very small in absolute terms (eg because of the units you have chosen to express the quantities at stake) but be very relevant for the modelling (and vice-versa).