A. Addition property of equality b. Identity property of addition
c. Division property of equality
d. Identity property of multiplication

A.
1: b
2: a
3: d
4: c
B.
1: a
2: c
3: b
4: d
C.
1: b
2: a
3: c
4: d
D.
1: a
2: b
3: c
4: d

Each person in an it department of 25 people works on at least one of 3 major projects: system security, program implementation, platform development. 10 people work on system security, 13 work on program implementation, and 12 work on platform development. 4 people work on system security and platform development, 5 people work on program implementation and platform development, and 2 people work on all three projects. how many people work on system security and program implementation?