A. There should be an apostrophe on the it's, because it is saying, "only some of it is clean and safe enough to drink." The apostrophe should be on that word because it breaks the word down into it is, which is correct in the sentence.
Answer:
Therefore, his theory of cognitive development suggests that developmental changes are discontinuous and occur in stages.
Explanation:
Psychologist Jean Piaget formulated the Theory of Cognitive Development. His theory suggests that developmental changes are discontinuous and occur in stages. Instead of there being a gradual, fluid process of development, in Piaget's theory children show different abilities according to the stage in which they are. Those stages are connected to their age, and the changes they bring are sudden. Therefore, there is a discontinuation, as if the second stage is supposed to happen at a certain time and in a certain manner, independently of the first stage, for instance. In his theory, there is a total of four developmental stages.
Most likely A.
In this case a simple statement could be any of those, to shorten to the simple statement you would generalize :)
