The most beautiful bird was flying . . . . . . . . the river. A. with B. on C. in D. across

The correct answer is D. across.

The word “across” means from one side of something to the other. In this case, the bird is flying from one side of the river to the other.

The other options are incorrect because they do not accurately describe the bird’s movement.

• The word “with” means together with. In this case, the bird is not flying together with the river.
• The word “on” means on top of. In this case, the bird is not flying on top of the river.
• The word “in” means inside of. In this case, the bird is not flying inside of the river.