Friendly, dangerous, modern, big, expensive, noisy, quiet.
Friendlier / more friendly, more dangerous, moderner / more modern, bigger, more expensive, noisier, quieter / more quiet.
The friendliest / the most friendly, the most dangerous, modern, the biggest, the most expensive, the noisiest, the quietest / the most quiet.
Некоторые прилагательные можно изменять двумя способами.