Cindy prepares burgers with two slices of beef each. A box of beef has $20$ slices. How many burgers can she prepare with all the three and a half box of beef? (Adapted from 2013 Math Kangaroo Problem, Level 3-4, Question \#7) 
选项为:A:$$10$$  B:$$35$$  C:$$45$$  D:$$25$$  E:$$30$$  请回答其中一个选项.