; and (2) an examination of hydrogen-natural gas blended pipeline systems currently operating, including in the United States, the United Kingdom, Canada, Europe, Australia, and Hong Kong. (c) Considerations In conducting the study under subsection (a), the Comptroller General shall consider— (1) any changes that domestic and international operators of natural gas pipeline systems have implemented to the processes, pipeline materials, metering, and operational standards used by such operators to account for the operation and integrity of natural gas pipeline systems that use a hydrogen content at variable percentages above 5 percent by volume; and (2) how such operators have taken into account the effects of hydrogen-natural gas blending on different types of— (A) natural gas pipeline systems materials, including cast iron, steel, composite pipe, and plastic pipe