Concept:The word filling the blank must agree with the singular noun "side" and express the idea that parking is allowed on one side or the other of the street.
Explanation:The word "all" is not suitable because it usually comes before a plural noun, such as "all sides".
The word "no" changes the meaning entirely and suggests that parking is not permitted anywhere, which does not fit the positive idea of "You can park".
The word "both" also requires a plural noun, so "on both side" would be grammatically incorrect.
The word "either" refers to one of two choices and is correctly used with a singular noun.
Thus, the sentence becomes "You can park on either side of the street".
This sentence correctly means that you may park on one side or the other of the two sides of the street.
Among all the given options, only "either" is both grammatically correct and logical in this context.
Answer:Option C: either