If applied to the text, which ones would be correct and keep the literal meaning...

Questão de Inglês da banca UFRGS aplicada no concurso UFRGS (2018). Confira a resolução completa abaixo:

Consider the following propositions for rephrasing the clause It could be argued that the answer is one (l. 19).
 I - One might argue that the answer is one. 
 II - You could say that the answer is one.
 III- They should argue that the answer is one.
If applied to the text, which ones would be correct and keep the literal meaning?