please correct my senetences

1. Social factors such as being part of a family network, having many friends, and participating in social activities are said in to contribute the to longevity.

2. Plankton, tiny plants that OR which drift along with the sea currents but are too small for the human eye to see, provides basic food for bigger sea animals.

3. Terrifying to see when rearing its upper body and head to an upright position to attack, the King Cobra is actually elusive in nature and only attacks when provoked.

Thanks :)

(Great sentences!!)