The correct answer is C. The government has announced that taxes will be raised.
The other options are incorrect because they do not use the correct verb tense. Option A uses the past tense, which is incorrect because the government has not yet raised taxes. Option B uses the past participle, which is incorrect because the government has not yet raised taxes. Option D does not use a verb, which is incorrect because the government has announced that it will raise taxes.
The government has announced that taxes will be raised. This means that the government has decided to raise taxes and has made an official announcement about this decision. The government has not yet raised taxes, but it has announced that it will do so in the future.