Try giving the paragraph a short title in your own words before choosing. The heading needs to cover its main point, not just a detail with the same word.
For example, a paragraph could mention a cheap train ticket but mainly explain why people stopped travelling by train. 'Reasons for declining rail use' would cover more of that paragraph than 'Affordable tickets'.
Fatima, do you get stuck between two headings too, or is it more about understanding the paragraph? I just posted about choosing between two because both can seem right to me