Option 1 states that agriculture is the only human activity considered as a source of greenhouse gases. This is incorrect because both fisheries and animal husbandry are also considered as sources of greenhouse gases.

Option 2 states that both fisheries and animal husbandry are sources of greenhouse gases. This is correct because these activities, particularly intensive farming and livestock rearing, can release significant amounts of methane, a potent greenhouse gas, into the atmosphere. Methane is produced by livestock during digestion and from the decomposition of organic matter in the water bodies where fisheries operate.

Option 3 states that agriculture and animal husbandry are considered as sources of greenhouse gases. This is correct because agriculture, including both crop cultivation and livestock rearing, can result in the release of greenhouse gases like methane and nitrous oxide.

Option 4 states that none of the activities mentioned are sources of greenhouse gases. This is incorrect as all three activities – agriculture, fisheries, and animal husbandry – contribute to greenhouse gas emissions.

Therefore, the correct answer is option 3: 1 and 3 are considered as sources of greenhouse gases.