高手解惑，怎样理解下面引文第三和第四中的问题

Don't use the superlative degree of the adjective for the comparative; as "He is the richest of the two" for "He is the richer of the two." Other mistakes often made in this connection are (1) Using the double comparative and superlative; as, "These apples are much more preferable." "The most universal motive to business is gain." (2) Comparing objects which belong to dissimilar classes; as "There is no nicer life than a teacher." (3) Including objects in class to which they do not belong; as, "The fairest of her daughters, Eve." (4) Excluding an object from a class to which it does belong; as, "Caesar was braver than any ancient warrior."