Practice forming the feminine and plural forms of adjectives.
The adjective "eficaz" doesn't change between the feminine and masculine forms.
Explanation
The adjective "pobre" doesn't change between the feminine and masculine forms.
Adjectives that end in "-z" in the singular form change the "-z" to a "-c" in the plural form.
Adjectives that end in a consonant add "-es" in the plural form.
Adjectives that end in a vowel add an "-s" in the plural form.
"Feo" is masculine adjective and "casa" is a feminine noun, so they don't match.