In an unbiased $n-p$ junction,electrons diffuse from $n-$ region to $p-$ region because

• A
  holes in $p-$ region attract them
• B
  electrons travel across the junction due to potential difference
• C
  only electrons move from $n$ to $p$ region and not the vice-versa
• D
  electron concentration in $n-$ region is more compared to that in $p-$ region