Was Crocodile stronger at Marineford? Or was he holding back in Alabasta?

 During the Alabasta arc, Crocodile displayed a level of power that was initially considered overwhelming by the Straw Hat Pirates. He possessed the Logia-type Devil Fruit called the Suna Suna no Mi (Sand-Sand Fruit), which granted him the ability to control and transform into sand. He had a reputation as a Shichibukai and controlled the desert kingdom of Alabasta from the shadows. His strength was showcased through his battles with Luffy and others. At Marineford, Crocodile was present as part of the war that took place at Marine Headquarters. While he did participate in the battle, he didn't display the same level of dominance as some other powerful characters present. This has led fans to speculate that he might not have been as strong as initially portrayed in Alabasta. It's important to note that power scaling and character abilities can be subject to interpretation and development by the author. Oda often keeps details deliberately open-ended to keep the story intriguing.

Who invented the train? Why is the train so useful to us?

 The first steam-powered locomotive was developed in the early 19th century by George Stephenson, a British inventor and engineer. Stephenson's locomotive, called the "Rocket," was designed to haul coal on the Stockton and Darlington Railway in England.

Trains are useful for a variety of reasons. One of the main benefits of trains is their efficiency and speed. Trains can travel long distances quickly, making them an effective means of transportation for both people and goods.

Trains are also an important part of many countries' transportation systems, as they can carry large numbers of passengers and goods over long distances. This makes trains an important means of connecting people and businesses, and they are often used to transport goods between cities and regions.

Trains are also considered to be more environmentally friendly than other forms of transportation, such as cars and airplanes, as they produce lower levels of greenhouse gas emissions. This makes them an attractive option for those looking to reduce their carbon footprint.

Overall, trains are a useful means of transportation for people and goods due to their efficiency, speed, capacity, and environmental benefits. The first steam-powered locomotive was developed in the early 19th century by George Stephenson.