Final answer:
The Beatles spent time performing in c. Hamburg, Germany, which was pivotal to their musical development and success.
Step-by-step explanation:
The German city where the Beatles spent a significant amount of time performing early in their career is c) Hamburg. This experience in Hamburg is often credited with being crucial to their development as musicians, exposing them to a wide array of musical influences and honing their performance skills.
Their time in Hamburg's vibrant music scene helped to lay the foundation for their later international success.