Thank you for your reply.
Lesson number 1
When a NOUN begins with a VOWEL use article 'an'
The NOUN 'undergraduate' begins with VOWEL 'u'
EXAMPLE... ''I am 'an' undergraduate.'' is correct
''I am 'a' undergraduate.'' is not correct
Correct English is not easy for Thai people.
English is AN International language.
I will help you more if you want.
Your teacher Frank xxx