How much alcohol must be in a driver's blood in order for them to be charged with driving while under the influence?

Answer: C — 0.08%

A driver can be charged with driving while under the influence if their blood alcohol level is at or above 0.08%. This is the legal limit for intoxication in most states. B, D and A are incorrect options as they all contain blood alcohol levels below the legal limit. While 0.07% and 0.09% may still result in impairment, they do not meet the specific threshold set by law for a DUI charge. 0.05% is even further below the legal limit and would not likely result in impairment.