Someone help me with this I will make you

Match the following: 1. empirical the belief that an idea should be evaluated based on how it works 2. fundamentalism knowledge based on observation and experiment rather than theory 3. obtrusive to intentionally force ideas or intrude on others 4. pragmatism not religious or spiritual in nature 5. secular a religious doctrine that emphasizes a return to rigid principles

Clouds thar look like whisps of hair are

Which of the following was probably the most difficult challenge facing construction of the railroad?