Is oxygen the only gas _______ helps fire burn?

The shoes are neither cheap nor comfortable, I can’t understand _______women like buying them .

He had to pause from time to time to wipe the sweat from his forehead, because the air-conditioning system _________.

Riding bikes has advantages __________ driving cars ________ many aspects

Zhong Nanshan, the famous medical scientist, has devoted most of his life ________ useful ways in treating cough diseases.