Identify the error in the sentence.
That was the worse movie I've ever seen.

Correct option is B

Option (b) contains an error.
Explanation of error: “Worse” is the comparative degree of bad, used for two entities. The structure “I’ve ever seen” signals selection from all experiences, demanding the superlative degree worst. The correct sentence is: That was the worst movie I’ve ever seen.
Grammatical rule used: Use comparative (-er/more) for comparison of two; use superlative (the -est/most) for selection from three or more/all. Irregular degrees: bad → worse → worst.
Example: This cake is good, that one is better, but the third is the best.
Information booster: Superlatives generally take the article the (e.g., the worst), and are frequent with “ever,” “of all,” “I’ve/you’ve/they’ve ever …,” etc.