The question asks about the specific forest areas that were threatened by a serious epidemic in 1997. This is a specific knowledge-based question and could not be inferred without prior information.

Option 1 suggests that teak forests in areas 3 and 4 were threatened. Option 2 claims the epidemic struck the oak forests in area 1 and sal forests in area 2. While option 4 cites that sandalwood forests in area 4 were affected.

However, the correct answer is option 3 which posits that the epidemic in 1997 hit specifically the sal forests in area 3. This could imply that the epidemic was either localized to this region and type of forest or that the sal trees in this area were exceptionally susceptible to the epidemic that occurred. The answer does not imply that other areas and types of forests were not affected, just that the given regions and types in options 1, 2 and 4 were not struck by the epidemic in the stated year.