Lexington senior Jenna Busa is a double threat. The All- Scholastic is not only one of the best pitchers in Eastern Mass., she is also a solid hitter. Busa's hitting (2 HRs, 6 RBIs, .586 average) is keeping Lexington in the hunt for the Middlesex League title. Busa is also on the field hockey and ice hockey teams. She has a fraternal twin brother, Andrew (she's older by 45 seconds). In this week's Q & A, Busa discussed everything from the her pitching arsenal to her most treasured possession. ON SOFTBALL Why is your number special? I wear No. 1 . . . but No. 21 is my favorite number. However, ...