The correct answer is option (B):
evergreen
The word "deciduous" refers to plants that shed their leaves seasonally, typically in autumn. This shedding is a natural process for many trees and shrubs. The opposite of this characteristic is for a plant to retain its leaves throughout the year, which is known as being evergreen. Therefore, "evergreen" is the correct answer because it describes the characteristic that is contrary to being deciduous.
Let's briefly look at why the other options are not suitable.
"Undecided" refers to a state of not having made a choice or decision, and it has no relation to botanical terms for plant leaf retention.
"Perennial" describes plants that live for more than two years. While many deciduous plants are perennial, and many evergreen plants are also perennial, "perennial" itself does not describe the shedding of leaves.
"Annual" describes plants that complete their life cycle in one year. Again, this is about the plant's lifespan, not its leaf retention.
Thus, "evergreen" is the direct antonym of "deciduous" in the context of plant foliage.