Ok if he/she is good friend and u really care foe them then try to knw why that person is being irregular for last few days/weeks. after knwng try to explain ur class teacher personally instead of going and tllng her in front of our whole class. make ur teacher convinced to support her/him for doing her absent work as fast as possible. make her feel comfortable and urself too has ur r goimg to tlk about her on behalf of his/her side. tll teacher tht because of her/his shy nature she/he was not able to tll her problm so i aftr knowing decided to help her/his wthout any fault. as the proverb goes like this that a friend in need is a friend indeed. mention this porverb too. i hoipe it would help u.
thank u. 
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