Two chemical species $X$ and $Y$ combine together to form a product $P$ which contains both $X$ and $Y$.
$X + Y \to P$
$X$ and $Y$ cannot be broken down into simpler substances by simple chemical reactions. Which of the following concerning the species $X$,$Y$ and $P$ are correct?
$(i)$ $P$ is a compound
$(ii)$ $X$ and $Y$ are compounds
$(iii)$ $X$ and $Y$ are elements
$(iv)$ $P$ has a fixed composition

• A
  $(i), (iii)$ and $(iv)$
• B
  $(i), (ii)$ and $(iv)$
• C
  $(ii), (iii)$ and $(iv)$
• D
  $(i), (iii)$ and $(iii)$