Wedding photography Xiaofeng Xiaoying

A. Method for checking the air tightness of the device: immerse one end of the catheter in water, and put your hands close to the outer wall of the container. The device will not leak if air bubbles emerge from the duct opening; On the contrary, the operation shown in the figure is correct.

B, when taking potions, the bottle stopper should be inverted, the label should be aimed at the palm of your hand, and the bottle mouth should be next to it. The operation shown in the figure is correct.

C, the density of oxygen is greater than that of air, and it should be collected by upward exhaust method, and the conduit should extend to the bottom of the gas container. The operation shown in the figure is correct.

D, when the oxygen is full, the wooden strip with Mars should be placed in the bottle mouth. The operation shown in the figure is wrong.

So choose D.