Martha said, “I am going to Mexico next year.”

The correct answer is: Martha said that she will be going to Mexico next year.

Martha’s statement is in the simple present tense, which indicates that she is making a plan or intention for the future. The other options are all in the past tense, which would indicate that Martha has already made the trip to Mexico or is no longer planning to go.

Here is a more detailed explanation of each option:

• Option A: Martha said that she had been going to Mexico next year. This option is incorrect because it uses the past perfect tense, which indicates that Martha had already made the trip to Mexico before the time of her statement.
• Option B: Martha said that she was going to Mexico next year. This option is incorrect because it uses the past progressive tense, which indicates that Martha was in the process of going to Mexico at the time of her statement.
• Option C: Martha said that she had gone to Mexico next year. This option is incorrect because it uses the past perfect tense, which indicates that Martha had already made the trip to Mexico before the time of her statement.
• Option D: Martha said that she will be going to Mexico next year. This option is correct because it uses the simple future tense, which indicates that Martha is planning to go to Mexico in the future.