Answer:
Because their economies have become weak, borrowing additional money to keep their governments going has become more costly, which has made their economies even weaker.
Explanation:
The Manhattan Project was the US government program during World War II that developed and built these first atomic bombs. Detonation of these first nuclear bombs signaled arrival of a frightening new Atomic Age.
Am irregular verb means that the different forms of the verb will differ and will not follow a regular pattern,
The pattern here should be:
I VERB, I VERB-ed, I will VERB
the first three options follow this pattern, so they are regular,
the correct answer is D. it is irregular: the past tense form is irregular.