Determining Useful Life,salvage Value and Required Provisions for Future Site

Multiple Choice

Determining useful life,salvage value and required provisions for future site restoration costs,all render valuation a high inherent risk assertion for the audit of PPE.What are the main reasons?

A) Annual depreciation expense is always a highly material amount.
B) There is a lack of independent evidence to support the assertion.
C) The high degree of subjectivity and potential for management bias.
D) Auditor reliance on an external expert is usually required.