以下过程一定存在反馈调节的是( )
①胰高血糖素分泌量对血糖浓度的影响
②运动强度对汗腺分泌的影响
③降雨量对土壤动物存活率的影响
④被捕食者数量对其天敌数量的影响
A:①②
B:②③
C:③④
D:①④
both different/the same both like each other always/usually/often ... play football/basketball... help people cross the street/carry the bags
I am…… .……is/are my good friend/friends. We ……
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(2016•内江)有学者认为,候鸟原本是沿捷近路线迁徙,后来由于地壳运动使候鸟的导航地面目标产生移动,从而使迁徙路线也随之变动,读图,候鸟从丙地向丁地迁徙,飞行的方向是( )