11.   Researchers worked to add to the arsenal, but their approach was hit-or-miss, relying more on happy accidents than on scientific acumen.

12.   Telomerase works to add a special ending to the DNA sequence found at the ends of chromosomes.

13.   Tucker said technicians were working to add more capacity to the system to accommodate the crush of users.

14.   What works, he added, is a system that puts the primary responsibility for education at the lowest possible level.

15.   When the performance works, she adds, it is equal parts of Tallulah and Kathleen.

16.   Scientists are working to add new functions to them so the robots can climb up and down a pipe while connected to other machines.