A is incorrect, because calcium hydroxide is slightly soluble in water, and the white solid may be undissolved calcium hydroxide, not necessarily calcium carbonate;

B is incorrect, because calcium oxide reacts with water to generate calcium hydroxide, so white solids do not necessarily contain calcium hydroxide. The chemical equation of the reaction between calcium oxide and water is: Cao+H2O-Ca (OH) 2.

Therefore, filling: calcium hydroxide is slightly soluble in water, and white solid may also be undissolved calcium hydroxide; CaO+H2 O═Ca(OH)2.

Experimental operation 2

1. Take out the sample and put it in a test tube filled with water. The increase in temperature indicates that the white solid contains calcium oxide.

Therefore, white solids contain calcium oxide.

2. Put the sample into a mortar and grind it with ammonium nitrate to produce a gas with pungent smell, which shows that the white solid contains calcium hydroxide.

So filling: produce gas with pungent smell.

3. Dropping dilute hydrochloric acid into the sample produces bubbles, indicating that the white solid contains calcium carbonate.

Therefore, white solids contain calcium carbonate.

Extension and application

From Xiaoyu experiment 2 (the sample is ground with ammonium nitrate), it can be seen that when applying ammonium nitrogen fertilizer, it should be noted that ammonium nitrogen fertilizer cannot be mixed with alkaline fertilizer to avoid reducing fertilizer efficiency.

Therefore, it should not be mixed with alkaline fertilizer.