The first formed primary phloem referred as...$A$... The later formed primary pholem is referred as ...$B$...

Choose the correct combinations of $A$ and $B$

• A

  $A$-protoxylem, $B$-metaxylem

• B

  $A$-protophloem, $B$-sieve tube cells

• C

  $A$-metaploem, $B$-sieve tube cells

• D

  $A$-protopholem, $B$-metaphloem