Thanks for the answer.

> why so? people was preoccupied with the higher costs to the standard/consumption engine
So people were preoccupied with higher cost, right?
And ignoring the pollution. So `ignorance of` would be the right answer?

The Wankel rotary engine was an engineering marvel that (i)_____ automobile exhaust emissions, but because it was less fuel efficient than the standard piston-cylinder engine, it was (ii)_____ in the early 1970s when (iii)_____ pollution gave way to panic over fuel shortages.

The phrase "gave way to panic over fuel shortages" indicates that earlier there must have been concern over pollution. Therefore, preoccupation with fits well in the blank.

Since the Wankel rotary engine is described as an engineering marvel, it should be something that reduced automobile exhaust emissions. The thought contrastor in "but because it was less fuel-efficient" further confirms this choice. The choice is substantially reduced.

Since in the early 1970s the preoccupation with pollution gave way to panic over fuel shortages, it must have been abandoned at that time.

Good question. Mainly the pollution but I assume is implied if you run away from an engine because it produces too much pollution there are also costs implied because the engine is less efficient.

Either way, people dismissed it because they were preoccupied.

Regards

First, I find the usage,

it was (ii) abandoned in the early 1970s when (iii) ignorance of pollution gave way to panic over fuel shortages.

very strange.

Second,

If the public were ignorant of pollution, they would never have chosen (and later abandoned) the Wankel engine. They would have gone for the more fuel-efficient and highly polluting standard piston-cylinder engine right from the beginning.

Hope that helps, if not ask again.

I misunderstood the last part of the sentence. I understand now after reading the explanations. Thanks to both of you!