Pick the change that is NOT unique to entering formal operations. (A) being able to logically argue both sides of an issue (B) being able to...

The formal operations stage of human cognitive development is the latest stage in Piaget's theory, and generally begins around the age of 11 or 12, shortly before the onset of puberty. During this stage, children acquire the capacity to engage in abstract reasoning, separating the concrete content of ideas from the abstract logical relations between them.Before the formal stage, kids learned to interact with the environment (sensorimotor stage), experience self-awareness and learn to speak...

The formal operations stage of human cognitive development is the latest stage in Piaget's theory, and generally begins around the age of 11 or 12, shortly before the onset of puberty. During this stage, children acquire the capacity to engage in abstract reasoning, separating the concrete content of ideas from the abstract logical relations between them.

Before the formal stage, kids learned to interact with the environment (sensorimotor stage), experience self-awareness and learn to speak language (preoperational stage), and finally to reason about the world in concrete terms (concrete operational stage). But it is not until the formal operational stage that children figure out how to separate the form of ideas from their contents.

A great example of a problem that kids get wrong in the concrete operational stage but get right in the formal operational stage is something like this:

Is this a valid argument? All whales are green and all green things are fish, therefore all whales are fish.

The answer is "yes"; this argument is formally valid. But in order to do that you've got to think of it in abstract terms like "all W are G, all G are F, therefore all W are F". If you were focused on the concrete stuff about whales and fish, you'd say it was invalid because whales aren't fish.

With all of this in mind, the best answer is clearly (D); while logical argument, scientific reasoning, and thinking about unreal ideas are all part of using formal reasoning and thus the formal operational stage, learning new words was something kids acquired a long time ago in the preoperational stage.