According to Euclid's division lemma,for given positive integers $a$ and $7$,there exist unique non-negative integers $q$ and $r$ such that $a = 7q + r$; where..........

• A
  $0 < r \leqslant 7$
• B
  $0 \leqslant r < 7$
• C
  $1 \leqslant r \leqslant 7$
• D
  $r \geqslant 7$