collection period (schweser)

This is concept check 5 in reading 46. Company’s weighted average collection period increases from 45 to 55 days. It’s average days of receivables decreases from 22 to 13 days. It is most likely that : a) Company relaxed it’s credit standards b) Fewer customers are taking advantage of discounts for early payment c) Credit customers are paying more slowly d) credit sales are a greater part of business this year. The answer is C. But I don’t understand the explanation. What about A? Isn’t increasing the loan length (say 30 to 60 says) be relaxing of credit? What about d?