In the following passage, some words have been deleted. Read the passage carefully and select the most appropriate option to fill in each blank.
The fire season that started in late 2019 in Australia (1) ________ massive devastation and things swiftly got worse before rains finally came and helped contain the (2) ________ fires ever. The smoke released by the fires became (3) ________ disaster. On January 1st, Australia's capital recorded the worst pollution it's ever seen, with an air quality index 23 times higher (4) ________ what's considered 'hazardous'. Smoke in the city crept into birthing rooms, stopped MRI machines from working, and (5) ________ a heart attack in one elderly woman who died soon after she stepped off a plane.

Select the most appropriate option to fill in blank no. 4.

1. A
   to
2. B
   than
3. C
   as
4. D
   by