Final answer:
Carl Siemens contributed to the Siemens-Martin process for steelmaking, which, along with the Bessemer process, was crucial for the mass production of steel during the Second Industrial Revolution.
Step-by-step explanation:
The invention that Carl Siemens contributed to that helped make the Second Industrial Revolution possible was the open-hearth process for steelmaking, also known as the Siemens-Martin process. This method, alongside the Bessemer process, revolutionized steel production, making it easier to produce high-quality steel in larger quantities. Steel became essential for the infrastructure of the time, fueling the construction of skyscrapers and the expansion of railroad networks.
While Sir Charles Parsons invented the steam turbine in 1884 and this was pivotal for generating electricity and powering ships, it was the mass production of steel using processes like the Siemens-Martin process that defined the era's industrial breakthroughs.
Thus, the correct answer to the student's question is C. Bessemer process, as it is closely related to the open-hearth process developed in part by Carl Siemens, both of which were integral to mass steel production.