Add punctuation: The following symptoms can be signs of stress poor concentration eating disorders frequent complaints of headache and stomach pain and continence problems
A: The following symptoms can be signs of stress: poor concentration, eating disorders, frequent complaints of headache and stomach pain, and continence problems.

Add punctuation: It leads to rain forest destruction global heat rising water pollution water scarcity desertification misuse of energy resources and world hunger
A: It leads to rain forest destruction, global heat rising, water pollution, water scarcity, desertification, misuse of energy resources and world hunger.

Add punctuation: 21 The Service can only be used once registration has taken place
A:
2.1 The Service can only be used once registration has taken place.