(____)1.A.pen B. pencil C. to
(____)2.A. run B. in C. walk
(____)3.A.ruler B. crayon C. flower
(____)4.A.easy B. this C. that
(____)5.A.here B. there C. book
质量70kg的消防员背负10kg的装备沿竖起金属杆匀速下滑,此时消防员所受的摩擦力大小是____N,方向是____.(g取10N/kg)
生物的多样性不包括( )