Our client currently has zero debt and is considering levering up to 40% debt-to-capital. How exactly would this affect their Cost of Equity and WACC? Will WACC keep decreasing forever as they add more debt?

我们的客户目前是零负债，他们正考虑加杠杆，把债务占资本比重提高到40%。这会如何影响他们的股权资本成本（Cost of Equity）和WACC？WACC会随着负债增加一直下降吗？