The correct answer is D
Camila y María son trabajadoras.
This is correct because...
A) trabajador
This is singular and masculine
B) trabajadores
Although this is plural, this is masculine which would be used if the sentence was talking about 2 males or 1 male and 1 female.
C) trabajadora
Although this is feminine, it is only talking about 1 female. The sentence is talking about 2.
D) trabajadoras
This is the correct answer because it is plural and feminine.