Which of the following expressions can be used to generate the string 'open quotation, happy, close quotation'?
1) 'open quotation' + 'happy' + 'close quotation'
2) 'open quotation' . 'happy' . 'close quotation'
3) 'open quotation' & 'happy' & 'close quotation'
4) 'open quotation' * 'happy' * 'close quotation'
