Explanation:

- Legitimacy means the legal status of being someone's lawful child.

- Presumptive marriage: Correct Answer

- The law often presumes legitimacy from a valid marriage—even if there are doubts about parentage.

- If a child is born during a lawful or presumptive marriage, the law presumes the husband is the father.

- Custom:

- Custom alone doesn’t usually prove legitimacy, unless recognized by law.

- School certificate:

- A school certificate is just a document and does not in itself create a presumption of legitimacy.

- None of these:

- Not correct, because presumptive marriage is recognized in law.