Texas faces all of the following environmental challenges in the 21st century EXCEPT:
a.
finding alternative medical facilities for current research facilities
b.
finding alternative energy sources to keep up with increased demand and environmental efforts
c.
conserving water supplies for an expected increase in the population.
d.
regulating and improving air quality

A - Finding alternative medical facilities for current research facilities.

Explanation:

In the 21st century, Texas is faced with varied environmental challenges owing to climate change and rapid population increase, among other factors. Some of the environmental challenges resulting from these factors include: finding alternative energy source (i.e. renewable energy) so as to keep up with the increasing demand and environmental effort to abate fossil fuel consumption; conserving water supply so as to meet the increasing demand for water due to rapid population growth; and regulating and improving air quality by resorting to clean and reliable energy, etc.

Clearly, it is evident that option A which is finding alternative medical facilities for current research facilities is not part of the environmental challenges faced by Texas in the 21st century. Thus, the answer to the question is A.