Explanation:

- The sentence with blank no. 3 is: "They (3)______ inspired by the Portuguese and the Dutch who were (4)______ a flourishing trade in spices and earning huge (5)______."

- The correct grammatical structure here requires the past tense to convey that the inspiring event happened in the past.

- Option 1, "had," would not be correct because it's usually used with another verb in past perfect tense, e.g., "had been."

- Option 2, "are," is present tense, which does not fit the context of past events described in the passage.

- Option 3, "was," does not agree in number with "They," which is plural, requiring a plural verb form.

- Option 4, "were," is the correct option as it matches the plural subject "They" and conveys the past tense consistency through the sentence.