i have a doubt,what is difference between ptrsites,and ptc sites,can you explain

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see,friends,i am sufering the net,i saw lots of advertisements about the ptr sites,whether it is true or scam sites,i cant understand? what is the difference between ptr and ptc sites,really giving money to us,if any one of you getting means please tell me clearly,because i am the beginner of the ptrand ptc sites.