What makes it easier to care an object down stairs than up stairs?

Which of these substances does not protect against invaders in the nonspecific immune response? a. saliva b. mucus c. tears d. urine

Is there any species that went extinct in recent years due to natural causes (not caused by human interaction). if so, what caused it?

Match the following items 1. rr 2. rr 3. identical alleles 4. unlike alleles 5. rr ()homozygous, recessive ()homozygous definition ()heterozygous, dominant cell ()heterozygous definition () homozygous, dominant cell