Hint: Verb tenses will tell us how an action relates to the flow of time. There are three main tenses: present, past and future tenses.
Here in this question simple past tense is used. So, we have to find the answer that represents the answer in the simple past form.
Option A) Was discover – is an incorrect answer because in the expression 'was discover', the main verb would be 'was' only and not 'was discover' and 'discover' will become an adjective. This will change the meaning of the statement. Hence, this is an incorrect answer.
Option B) Was discovered – is the correct answer because ‘was discovered' is in the simple past tense. Thus, it states the fact and is the correct answer.
Option C) Found – is an incorrect answer because the sentence is in the passive voice, using 'found' will indicate that 'America' is carrying out the action. This will change the meaning of the sentence. Hence, It is an incorrect answer.
Option D) Had found – is not an incorrect answer because the sentence is in the passive voice, using 'had found' will indicate that 'America' is carrying out the action. This will change the meaning of the sentence Hence, It is an incorrect answer.
Hence the correct option is option ‘B’ i.e, “America was discovered by Christopher Columbus in 1492”.
Note:In such questions it is very important to understand the tenses. Here, the sentence tells us about a point in the past in 1492 when Christopher Columbus found America. Thus, the answer must be in the simple past tense. The best way to memorize verb tenses in the following formula: Personal pronoun + tense form (I write, he writes, we write, you write, etc.) Memorizing tense forms in such constructions will also help you to memorize basic subject-verb agreement in person and number.