Question

primary air quality standards are designed to protect the health of dropdown.
people with asthma can expect clean air under the dropdown standards in the clean air act.
dropdown air quality standards provide protection of public welfare.
dropdown are covered under the acts secondary air quality standards.

Explanation:

Define primary standards

Primary air quality standards protect public health.
This includes sensitive populations like asthmatics.

Identify first blank

The first blank completes "protect the health of".
The standard target is "sensitive populations".

Identify second blank

Asthmatics are protected under primary standards.
Thus, the second blank is "primary".

Define secondary standards

Secondary standards protect public welfare.
This includes visibility, crops, and vegetation.

Identify remaining blanks

The third blank is "Secondary".
The fourth blank is "Crops and vegetation".

Answer:

Primary air quality standards are designed to protect the health of <blank>sensitive populations</blank>.
People with asthma can expect clean air under the <blank>primary</blank> standards in the Clean Air Act.
<blank>Secondary</blank> air quality standards provide protection of public welfare.
<blank>Crops and vegetation</blank> are covered under the act's secondary air quality standards.