I . . . . . . . . a new job today. A. was joining B. am going to join C. will be join D. none of these

The correct answer is: B. am going to join

The sentence is in the present progressive tense, which is used to talk about actions that are happening or will happen in the near future. The other options are not in the present progressive tense, so they are incorrect.

• A. was joining is in the past progressive tense, which is used to talk about actions that were happening at a specific time in the past.
• C. will be join is in the future tense, which is used to talk about actions that will happen at a specific time in the future.
• D. none of these is not a grammatically correct sentence.

Here is a more detailed explanation of each option:

• A. was joining is in the past progressive tense. This tense is used to talk about actions that were happening at a specific time in the past. In this case, the action is “joining a new job.” The sentence would be correct if it said, “I was joining a new job yesterday.” However, the question is about what the speaker is doing today, so the past progressive tense is not appropriate.
• C. will be join is in the future tense. This tense is used to talk about actions that will happen at a specific time in the future. In this case, the action is “joining a new job.” The sentence would be correct if it said, “I will be joining a new job next week.” However, the question is about what the speaker is doing today, so the future tense is not appropriate.
• D. none of these is not a grammatically correct sentence. The verb “join” must be conjugated in the present progressive tense to agree with the subject “I.” The correct sentence would be, “I am going to join a new job today.”