Final answer:
Blade-type fuse holders are considered obsolete and unsafe. Modern fuse holders, such as cartridge-type and plug-type, are more commonly used and considered safer.
Step-by-step explanation:
Blade-type fuse holders are considered obsolete and unsafe. They are designed to hold blade fuses, which are flat and have two metal prongs on the sides. However, these fuse holders can easily get damaged or corroded, leading to poor electrical connections and potential safety hazards.
On the other hand, modern fuse holders, such as cartridge-type and plug-type, are more commonly used and considered safer. Cartridge-type fuse holders are designed to hold cylindrical fuses with metal end caps. Plug-type fuse holders allow fuses to be easily inserted and removed, ensuring a secure connection.
Therefore, the correct answer is (d) Blade-type.