The seashells were iridescent in the sunlight.

a. cloudy
b. drying out
c. breaking into pieces
d. shimmering with colors

I choose "d" Am I right?

If you are referring to the meaning of iridescent, yes, it's "d,"

Yes, you are correct! The seashells were iridescent in the sunlight means that they were shimmering with colors. Well done!

Yes, you are correct! The word "iridescent" means exhibiting a play of colors that seems to change as the angle of view or the angle of illumination changes. In the given sentence, it mentions that the seashells were iridescent "in the sunlight." This suggests that the seashells were shining and reflecting different colors when exposed to the light. Therefore, option d, "shimmering with colors," is the most suitable choice as it accurately describes the appearance of the seashells in the given context.