Rockwell's art an iconic symbol to many americans.
choose the verb that expresses an occurrence that began in the past and continues presently.
a) become
b) has become
c) is becoming
d) has been becoming

The verb that expresses an occurrence that began in the past and continues presently is B. has become. Rockwell's art has become an iconic symbol to many Americans. The answer here should be obvious - if the action started in the past, and continues into the present, you need a tense that connects both the past and the present, and that is the present perfect tense, or in this case, HAS BECOME, which is the present perfect form of the verb to become.