Correct Answer: constraint

Solution : The correct choice is the third option .

A constraint is a limit or restriction. This helps convey that although the effects of rising aviation industry emissions have been known for decades, they are still growing without any limits.

The meanings of the other options are as follows:

• Easiness is the quality of being comfortable.
• Neglect means to give less or no attention to something.
• Comfort is a state of ease.

Therefore, the complete sentence is: "The reality of the effects of rising aviation industry emissions on climate change has been known for decades, yet the industry and its emissions have continued to grow without constraint ."