
Present tense of the verb be and the โing form of a verb:
present simple
present continuous
present perfect simple
present perfect continuous
This form of present tense uses have/has + been and the -ing form of a verb:
present simple
present continuous
present perfect simple
present perfect continuous
This form of present tense uses have/has and the past participle of a verb:
present simple
present continuous
present perfect simple
present perfect continuous
He _____________________ to be a doctor for two years.
have been studying
has been studying
have studied
has studied