That sack is … heavy for us to lift

Analyze the question: The sentence is "That sack is __ heavy for us to lift." We need the word that fits the structure "heavy for us to lift."

Explain the concept: The structure too + adjective + (for someone) + to + verb expresses a negative result. It means something is more than what is needed or possible, so the action cannot be done.

• "too heavy for us to lift" means we cannot lift it.

Compare the other options:

• very heavy: describes the degree only, and it does not go with "to lift" to show a result. We would say "very heavy, but we lifted it."
• so heavy: needs "that" (so heavy that we could not lift it). It does not work with "for us to lift."
• quite heavy: means fairly heavy. It does not show that the action is impossible.

Solution:

1. The sentence ends with "for us to lift", an infinitive phrase showing the result.
2. The pattern "too + adjective + for + person + to + verb" fits perfectly.
3. "That sack is too heavy for us to lift" means the sack is so heavy that we cannot lift it.

Answer: C. too.

Tip: When you see "____ + adjective + to + verb," think too. Remember "so... that" and "too... to" as fixed pairs:

• The sack is so heavy that we cannot lift it.
• The sack is too heavy to lift.