A:i
B:with
C:by
D:at
—Indeed! One more step and he ________ off the cliff(悬崖).
①干冰的升华; ②硫酸钾熔化; ③NaCl溶于水; ④HCl溶于水; ⑤液氨的受热蒸发; ⑥Na2O2溶于水
在青藏铁路沿线能看到的景观有( )