Write S or F to identify each group of words as a sentence or a sentence fragment.
Wish on that star.
I think it is a sentence fragment (f)
http://www.studyzone.org/testprep/ela4/o/typesofsentencesl.cfm
To determine whether "Wish on that star" is a sentence or a sentence fragment, we need to understand the definition of a sentence. A sentence is a grammatically complete group of words that expresses a complete thought.
In this case, "Wish on that star" expresses a complete thought, indicating an action or command to "wish on that star." Therefore, "Wish on that star" is indeed a sentence. The correct answer is S (for sentence), not F (for sentence fragment).