The information below is extracted from the 2022 Sustainability Report of Woodside Ltd. Woodside is a hydrocarbon energy business, with a focus on natural gas. It is Australia's largest producer and exporter of natural gas, having merged with BHP Petroleum during 2022. PwC provided the 2022 financial report audit for Woodside. The financial report audit for 2021 had been provided by EY.

Woodside also issues a Sustainable Development Report, which has multiple parts, similar to BHP Ltd. Deloitte (one of the Big 4) provide limited assurance on selected subject matter from the report, including health and safety, people and environmental performance data. Separately, reasonable assurance is provided by GHD, an engineering consulting company, on Woodside's Scope 1 and 2 greenhouse gas emissions. In addition, an entity called "Business 4 Societal Impact" (B4SI) provide a "verification statement" of Woodside's community investment, which they state is "not an independent audit of the data". This statement appeared for the first time in 2022. Required:

(a) Why is there a demand for, and supply of, assurance on emerging external reports [EER] such as Woodside's sustainability report?

(b) Analyse why the different levels of assurance (limited and reasonable) have been given to the different areas of Woodside's sustainability operations in the conclusions outlined above.

(c) In your opinion, what is the single most challenging aspect of assuring sustainability information? Explain your reasoning.

(d) Critically analyse why Woodside may be getting its sustainability assurance from two different assurance providers: a Big 4 accounting firm and an engineering consulting firm, both of whom are different to its financial report auditor.