Which of the following does not tend to weaken buyer bargaining power?
a. Buyer demand is weak in relation to the available supply and industry members are eager to sell more units
b. Buyers have insufficient "prestige" to command special treatment
c. Buyer costs to switch to competing brands or to substitute products are relatively high
d. There are so many buyers that any one buyer's purchases account for a tiny fraction of total industry sales
e. Buyer sensitivity to price is low, often because the products/services of industry members are strongly differentiated and buyers have a strong attachment to a favourite brand