Learn French: Les résultats sont bons, donc la méthode est parfaite. - The results are good, therefore the method is perfect.

Both donc and alors can translate to 'so', but donc strongly emphasizes a logical conclusion or deduction ('therefore'). Because the speaker is making a direct logical deduction—the results are good, therefore the method is perfect—donc is the most natural fit here.

Why is the adjective bons used instead of the feminine bonnes?

Adjectives must match the gender and number of the noun they describe. Here, bons describes les résultats. Since un résultat is a masculine noun, we use the masculine plural form bons.

Why does parfaite end in an 'e'?

It describes la méthode, which is a feminine noun (indicated by la). We have to add an 'e' to the basic masculine form parfait to make it agree with the feminine noun.

Do you pronounce the 'c' at the end of donc?

Yes, the 'c' in donc is pronounced like a 'k' sound. Unlike many French words ending in consonants, you usually pronounce the 'c' in donc even when the next word starts with a consonant, as it does here with la.