When is rivalry in the industry likely to be higher?

Select one:

$$ a$.$ There is fast market growth and competitors are eager to capture a large share of the extended market;

b$.$ The products in the industry are highly differentiated, with many of them serving small niche customer segment

c$.$ The industry consists of many firms with substantial excess capacity

d$.$ The industry has low exit costs for the existing rivals, but high entry costs for the potential new entrants