In a fear conditioning procedure, a compound stimulus consisting of a light and a bell is repeatedly paired with a shock that can support a maximum associative value of 20. According to the Rescorla-Wagner theory, if the light had previously acquired 20 units of associative value, then the bell will acquire ____ units, which is an example of ___.

a. 0; blocking

b. 20; blocking

c. 20; the overexpectation effect

d. 0; overshadowing