The correct answer is: B. written
A tacit agreement is one that is not explicitly stated, but is understood by both parties. A written agreement, on the other hand, is one that is formally documented.
Option A, “order,” is not an antonym of “tacit.” An order can be either tacit or explicit. For example, if you tell your child to go to bed, that is an explicit order. However, if you simply look at your child and raise your eyebrow, that could be a tacit order to go to bed.
Option C, “oral,” is also not an antonym of “tacit.” An agreement can be either tacit or oral. For example, if you shake hands with someone, that is an oral agreement. However, if you simply nod your head in agreement, that could be a tacit agreement.
Option D, “understanding,” is not an antonym of “tacit.” Understanding can be either tacit or explicit. For example, if you understand that your child is tired and needs to go to bed, that is an explicit understanding. However, if you simply sense that your child is tired, that could be a tacit understanding.
In conclusion, the only option that is an antonym of “tacit” is “written.”