There one star on the wall.
A:is
B:are
C:have
——Don't open the door, _______who knocks on it.——No problem, mom. You've told me many times.
Can I help you?
已知白磷和红磷的着火点分别为40℃、240℃.某学习小组按照图所示装置去探究燃烧的三个条件,通过多次实验,他们对燃烧的三个条件始终未能探究全面,你认为他们不能探究到的燃烧条件是____.