The answer is the first one (A): Desktop computers.
Explanation for each option:
A. Desktop computers: Desktop computers are generally the easiest to upgrade. They have larger cases that are designed to be opened easily, allowing users to add or replace components like RAM, hard drives, graphics cards, and more. The internal components are often standardized, making it straightforward to find compatible parts.
B. Tablets: Tablets are typically not designed for user upgrades. They have compact and integrated designs, with components like RAM soldered onto the motherboard, making it difficult or impossible for users to upgrade them.
C. Smartphones: Similar to tablets, smartphones are not designed for user upgrades. Their compact and integrated design means that components like RAM are soldered onto the motherboard, and opening the device can be challenging and may void warranties.
D. Laptops: While some laptops allow for upgrades, such as adding more RAM or replacing storage drives, they are generally more difficult to upgrade than desktop computers. The process can vary significantly between models, and some modern laptops have components soldered in place, limiting upgrade options.
In summary, desktop computers are the easiest to upgrade due to their design and accessibility to internal components.