Hi !
Let's take them one at a time :
A. Add -es if the noun ends in -o , -x , -s , -ss , -sh (ex:tomato -> tomtoes). There are quite a few nouns.
B.Change the y to i only if the nouns ends in y and there is a consonat before ( ex : butterfly -> butterflies ) . VERY FEW NOUNS
C.Almost the same thing as in B.
D.You can add -s to all the nouns that aren't end in -s,-o,-ss,-x,y,-sh and so on.ALMOST ALL THE WORDS.
So,the most common rule is D. adding -s to the word.
Have a nice day !