A reproductive barrier keeps similar species from interbreeding.
I would say D.....................
Syntax is also collectively known the arrangement of words in a sentence. The correct answer to your questino is B. For that reason it isn't possible for any other answer in this case to be correct because B actually denotes a rather formal way of how you could talk about syntax.
A right circular cylinder
I am pretty sure that a point mutation that creates a premature stop codon is called a synonymous mutation. It also can be called silent mutation, if you have it in you option list, feel free to use it, it is the same. That will definitely help you.
