A. Let's evaluate whether each group of words makes sense as a sentence:
Mango fall sky. - This group of words does not make sense as a sentence. A sentence should convey a complete thought, and this does not.
Mona writes a letter. - ✔ This is a complete sentence. It has a subject ('Mona') and a predicate ('writes a letter') that together convey a complete idea.
Playing students the are. - This does not make sense as a sentence. The words are jumbled, and the sentence does not convey a clear idea.
Always respect your elders. - ✔ This is a complete and meaningful sentence. It gives advice or instruction.
Road walk of that us. - This group of words does not form a meaningful sentence. It lacks clear structure and meaning.
Sita sings a song. - ✔ This is a well-structured sentence with a subject ('Sita') and a predicate ('sings a song') that express a complete thought.
Happy in wall black. - This does not make sense as a sentence. The words do not form a clear and complete idea.
Monika is a teacher. - ✔ This is a complete and meaningful sentence. It describes a fact about Monika.
B. Rearranging the words to form complete sentences:
useful animal is a ox the - The rearranged sentence is: The ox is a useful animal.
am I boy a - The rearranged sentence is: I am a boy.
play we cricket - The rearranged sentence is: We play cricket.
book this my is - The rearranged sentence is: This is my book.
shirt red is his - The rearranged sentence is: His shirt is red.
boarded he the bus - The rearranged sentence is: He boarded the bus.
Each rearranged group of words now forms a sentence that starts with a capital letter and ends with a full stop, adhering to proper sentence structure and conveying clear meanings.