डॉग स्पाइक्स (Dog spikes) का उपयोग आमतौर पर किस प्रकार के रेलवे स्लीपरों के साथ किया जाता है?

Which type of railway sleeper generally offers the longest service life under heavy axle loads?

A welded rail joint is generally:

Consider the following pairs regarding railway track components and their respective engineering functions/tools: i. Ballast — 1. Rail fastenings used with concrete sleepers ii. Sleeper — 2. To hold the rails in proper gauge alignment iii. Jim Crow — 3. Heavy tool used to bend rails accurately iv. Pandrol Clip — 4. To provide a load-distributing cushion effect to the track structure Which of the combinations given below correctly matches the component/tool with its primary description?