Is it a panda?- Yes, it ____ (is, isn't).
为了安全,列车进入隧道前必须鸣笛,若列车速度为72km/h,司机在鸣笛2s后听到从隧道口山崖反射的回声,则鸣笛时列车距隧道口 ____ m,已知声音在空气中的速度是340m/s.
①—Who is he?
—He's my father.
②— Who is she?
— She is my grandmother.
③—Who is she?
—She's my mother.
④—Who is he?
—He's my grandfather.
____