Explanation:

- Consent to cause death:

- The law generally does not allow individuals to consent to acts that result in their own death.

- Such consent is not a valid defense in legal cases involving death.

- Consent to cause grievous hurt:

- Consent is not a defense in cases involving grievous bodily harm.

- It often involves serious injuries which the law aims to prevent, regardless of consent.

- Option 3 - Both (a) & (b):

- This option states that consent is unavailable as a defense in both causing death and grievous hurt.

- It reflects the law's protective stance against severe harm and fatal outcomes.

- Option 4 - Either (a) or (b):

- Suggests that consent might be a defense in one of the situations, which is not typically the case.

Option 3 is correct:

- Cause death and grievous hurt are those scenarios where consent is not an available defense.