Step 1: Identify the tense.
The helping verb “has” indicates the present perfect tense. In this tense, the structure is:
has/have + past participle (V3)
Step 2: Choose the correct verb form.
The past participle form of “appear” is “appeared.” Therefore, “has appeared” is correct.
Step 3: Analyze the options.
- (a) appears: Simple present tense — incorrect.
- (b) will have appeared: Future perfect tense — incorrect.
- (c) appearing: Present participle — incorrect form.
- (d) appeared: Past participle — correct form to follow “has.”
Step 4: Constructing the correct sentence.
“The moon has not yet appeared.”
Step 5: Conclusion.
Therefore, the correct answer is (d) appeared.