In a bread recipe, the number of cups of flour should be a non-negative rational number. Let's evaluate the options:
A. 4/7 - This is a positive rational number and could specify a quantity of flour.
B. 2 3/4 - This is a positive mixed number and could specify a quantity of flour (equivalent to 2.75 cups).
C. -3 - This is a negative number and cannot specify a quantity of flour, as you can't use a negative amount.
D. square root of 3 - This is an irrational number (approximately 1.732) and wouldn't be a typical measurement for cups of flour in a recipe, which are usually specified in rational numbers.
Based on this analysis, the valid choices for specifying how many cups of flour should be used are A (4/7) and B (2 3/4).