Well, you need an aberration rubber tube when inserting the rubber plug, just like the glass tube of Xinjiang water tank. Do you know that?/You know what?

A, slowly turn the rubber stopper into the test tube mouth. Never put the test tube on the table and force it into the plug to avoid crushing the test tube. The operation shown in the figure is wrong.

B. When connecting the catheter to the rubber tube, first wet one end of the catheter, and then gently rotate it to insert it into the rubber tube. The equipment shown in the picture is correct.

C. 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. If there is air bubble at the catheter mouth, the device will not leak; The operation shown in the figure is correct.

D, slowly turn the rubber stopper into the test tube mouth. Never put the test tube on the table and force it into the plug to avoid crushing the test tube. The operation shown in the figure is correct.

So choose: a.