A、The oldest living things on Earth. B、How the drought is formed. C、Ways to help sequoias survive. D、Whether they should cut dow

California continues to suffer under a historic drought. The state has received very little rainfall over the past four years. California is famous for its huge sequoia trees. They are among the largest and oldest living things on Earth. But scientists say the trees are suffering because of the lack of water.
Now the National Park Service is studying how the drought has affected the sequoias and what can be done to help them survive. Researchers are using scientific equipment in the tree canopies to help measure air temperature and humidity levels. They also are studying sequoia seedlings, information from individual trees and images collected by aircraft to measure the seriousness of the danger. One possible solution would be to cut down less important tree species because other plants compete with the sequoias for water. Scientists say the sequoias will probably survive this drought, unlike many other California trees.
1.  What is the problem of California?      
2.  What does the National Park Service study?