The correct option is A a
Let’s examine the sentence: “Life on board ship was not as I expected it to be.” The sentence should have the indefinite article ‘a’ between ‘board’ and ‘ship.’ Otherwise, the sentence is not conveying any meaning in its first part. The article ‘a’ connects the phrase ‘on board’ with the noun ‘ship.’ So, the error is in Part A of the sentence. Hence, Option A is the correct answer.