A is exhibited only when two are present together. recessive allele

hybrid

purebred

dominant allele

I believe it's a dominant allele

Explanation:

Recessive allele means one is present... A hybrid is the result of two different breeds breeding. A purebred is an organism that always passes down the same genetic makeup.

"d.) carbon dioxide and hydrogen sulfide"

answer: national resource conservation services

national resource conservation services is the us. based approach that provides technical and financial assistance for natural resource management. nrcs society in conservation of resources by involving in activities like farmland protection, flood prevention, watershed protection, urban conservation, conserves economic and environmental conditions. it conducts soil surveys and implements the policy of natural resources management on the society.