Learn French: L'Amérique du Nord et l'Amérique du Sud sont très grandes.

In French, you usually cannot drop the main noun when referring to two distinct entities. Because North America and South America are separate continents, you must state both fully as l'Amérique du Nord and l'Amérique du Sud.

Why use du instead of de before Nord and Sud?

Compass directions are masculine nouns in French, so they take the article le (e.g., le nord). When you say 'of the North', the preposition de combines with le to form the mandatory contraction du.

Why is the adjective grandes feminine plural when Nord and Sud are masculine?

The adjective grandes describes the subject of the sentence, which is the continents themselves. Since the word Amérique is feminine, combining two feminine subjects results in a feminine plural adjective, regardless of the masculine words Nord and Sud right before the verb.

Why are the words Nord and Sud capitalized in this sentence?

Generally, compass points are lowercase in French. However, when they are part of a proper noun representing a specific geographical or political region, like the names of these continents, they are capitalized.