Final answer:
Using standard student microscopes, typically the nucleus is the only structure among those listed that is visible due to its relatively large size compared to actin filaments, microtubules, endoplasmic reticulum, and the Golgi apparatus.
Step-by-step explanation:
When using student microscopes in a lab setting, visible structures would typically include larger cell features such as nuclei, but actin filaments, microtubules, endoplasmic reticulum, and the Golgi apparatus are usually too small to be seen with standard school microscopes, which lack the magnification and resolving power of more advanced electron microscopes. However, the question specifies the visibility through student scopes at lab tables, so we can assume that simpler light microscopes are being used rather than electron microscopes. Among the given options, the nucleus stands out as the structure that is typically large enough to be visible under these conditions.