The specific cost of each source of long-term financing is based on __________ costs.

• before-tax and current
• after-tax and historical
• after-tax and current

Please also give me an explanation as I want to understand this concept between historical, current, before-tax and after-tax in relation to specific cost of sources in long-term financing. I think it is after-tax and historical, but it is only a guess and not a definitive answer.