What is the default reference implementation of Python written in the C programming language?

The default reference implementation of Python, known as CPython, is indeed written in the C programming language. CPython serves as the standard implementation that most people refer to when they talk about Python. It compiles Python code into bytecode, which is then interpreted by the Python virtual machine. This allows for high performance and seamless integration with C libraries. CPython promotes consistent behavior across different platforms, making it the go-to choice for Python developers and the basis for various Python distributions.

The other options refer to different implementations or variations of Python, but they serve different purposes. For instance, Jython allows Python code to run on the Java platform by transforming Python code into Java bytecode. PyPy is an alternative implementation of Python designed for speed and efficiency through techniques like Just-In-Time (JIT) compilation, while Pike is not a Python implementation; it is an entirely different programming language. Thus, CPython stands out as the primary and foundational implementation of Python, which is why it is the correct answer.