The correct answer is B. life.
Metal sleepers are superior to wooden sleepers in terms of life. Metal sleepers can last for up to 100 years, while wooden sleepers typically only last for 20-30 years. This is because metal sleepers are not susceptible to rot or decay, and they are also more resistant to fire and vandalism.
Metal sleepers are also more durable than wooden sleepers. They can withstand heavy loads and extreme weather conditions, and they are less likely to be damaged by derailments or other accidents. This makes them a more reliable choice for railway tracks.
In addition, metal sleepers are easier to maintain than wooden sleepers. They do not require regular painting or treatment, and they are less likely to need to be replaced. This makes them a more cost-effective choice in the long run.
However, metal sleepers are more expensive than wooden sleepers. They also require more specialized tools and equipment to install, which can add to the cost of construction. Additionally, metal sleepers can be more difficult to recycle than wooden sleepers.
Overall, metal sleepers are a superior choice to wooden sleepers in terms of life, durability, and ease of maintenance. However, they are also more expensive and require more specialized installation.