कौन सा प्रमुख कारक मुख्य रूप से कई विकासशील देशों में हवाई परिवहन बुनियादी ढांचे के व्यापक विस्तार को सीमित करता है?

Border roads are primarily considered highly vital because they:

Which railway gauge width is standardly classified and used as the 'Standard Gauge' in the United Kingdom?

Which of the following descriptions best defines the term 'highways'?