help me to change be engish!!!

Apple changes to yellow, this process is known as oxidation.
Many people think that apple changes to yellow is due to the Iron inside it oxidized. In fact, this is wrong. (I suppose everyone didn't eat any rusting iron when eating an apple.)
Actually, the substance causing oxidation is Phenol compound. When Phenol compound combines with the oxygen in the air, oxdation occurs. Therefore, some coloured substances will produce which made the apple turns yellow.
Anyway, you can use any method you like to reduce the apple in contact with the air(Oxygen), so this can slow down the apple turns to yellow.
Normally, sugar solution and salt solution contain fewer oxygen, thus they can reduce the pace of oxidation sharply.

An apple change its colour to yellow due to oxidation.

Many people think that apples turn yellow since the "iron" of the apple is oxidized, but this is wrong (I believe that nobody eat rust when eating an apple, right?!)!

The chemical being oxidized is Phenol compound. When this enzyme have contact with the Oxygen in air, oxidation occurs, and coloured substance appears on the surface, which makes apples turn yellow.

Any methods to lessen the chance for the apple to connect with Oxygen in air will slow down the process of turning the apple yellow. Since sugar or salt solution ahve lesser oxygen indensity, therefore, it can slow down the process effectively.