Please help me with these two questions. Thank you.<br/><br/><br/><br/>What are the differences between a. and b.??<br/><br/>a. I had never used that computer program.<br/><br/>b. I haver never used that computer program.<br/><br/>Which one is correct c or d and please explan the reason why. <br/><br/><br/><br/>c. I had never used that computer program before.<br/><br/>d. I haver never used that computer program before.