Cilia and flagella are outgrowths of

Cilia and Flagella are Filamentous Extensions which project outwards from the cell wall, Cilia and flagella are made up of microtubules and are covered by the tube membrane and the internal structure of both cilia and flagella are analogous. The collaboration between the microtubules in cilia and Flagella is very important for their movement. 
- Option(A) Cilia and Flagella are extensions of the cell wall; thus, this is the Correct option. 
- Option(B) Cilia and Flagella aren't extended from the nexus and thus, this is an Incorrect option. 
- Option(C) Since one of the options is correct, thus this is an Incorrect option. 
- Option(D) Since only one option is correct from the two options and not both of them are correct, thus this is an Incorrect option.

Hence, option A is the correct answer.