In each of the questions given below, four sentences are provided. One of the four sentences contains a grammatical error. Identify the sentence that contains the error. If all sentences are grammatically correct, select 'All are correct' as your choice.

The correct answer is: "The container had a tear, which letting the flour to spill out."

Detailed Step-by-Step Explanation:

To identify the sentence with a grammatical error, let's analyze the grammatical structure of each given sentence option:

1. "Advocates value the project for its ability to raise national revenue."
- Subject-verb agreement: The plural subject "Advocates" correctly matches the plural verb "value".
- Pronoun usage: The possessive pronoun "its" correctly refers back to the singular noun "project".
- Infinitive phrase: "to raise national revenue" is properly formed.
- Status: Grammatically correct.

2. "The initial recipient of the IMF grant was Belgium back in 1950."
- Subject-verb agreement: The singular noun phrase "The initial recipient" correctly matches the singular past tense verb "was".
- Prepositional usage: Time and object references ("of the IMF grant", "back in 1950") are standard and correct.
- Status: Grammatically correct.

3. "The container had a tear, which letting the flour to spill out."
- Error 1 (Incorrect Verb Form in Relative Clause): The relative clause introduced by the relative pronoun "which" requires a main finite verb (such as past tense "let" or "allowed") rather than a present participle ("letting").
- Error 2 (Incorrect Complement Structure): The verb "let" takes a bare infinitive (an infinitive without "to"). Therefore, "letting the flour to spill" is double ungrammatical. The verb "allow" takes a full infinitive with "to", whereas "let" takes just the base verb (e.g., "let the flour spill").
- Corrected Sentence: "The container had a tear, which let the flour spill out." OR "The container had a tear, which allowed the flour to spill out."
- Status: Contains grammatical errors.

4. "Trauma during youth can lead to severe anxiety later in life."
- Structure: The modal auxiliary "can" is followed by the base verb "lead", forming the prepositional phrase "lead to..." correctly.
- Status: Grammatically correct.

Conclusion:
Since sentence 3 contains clear structural and grammatical errors, it is the correct choice.