Which question below is impossible to test through observation? What is the average amount of acorns squirrels living in a park collect in fall?
Which foods did dinosaurs compete for?
Which bird species migrates in winter?
Which type of flower in a field stays in bloom the longest?

true, i don't really know what you're asking but from the info you provided im guessing the answer is true.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".

c should be the answer

the correct answer is option d.

an appositive is a noun, noun phrase or noun clause which follows another noun or noun phrase in order to describe it or name it another way. they are usually used between commas, brackets or dashes.

the example sentence with the correct use of commas is the following:

her uncle, the man over there in the red shirt, owns the hardware store in town.