" That's only true for tough adjectives. 'easy' and 'difficult' are tough adjectives. 'weak' is not.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
AnonymousSomewhere I read this kind of rules - "you cannot use passive infinitive if it is to be followed by an adjective."That's only true for tough adjectives. 'easy' and 'difficult' are tough adjectives. 'weak' is not. So your 1 and 2 are correct, but your 3 is wrong. Both sentences in 3 are correct.