When do I need to add annotation when I use Hilt as dependency injection?

Question

I'm reading the article Using Hilt in your Android app.

The Code A, Code B and Code C are from the sample project in solution branch.

I'm confused when I should add the Hilt annotation.

1. In Code A, the parameter database of fun provideLogDao is injected, but the author doesn't add any annotation, but the parameter appContext of fun provideDatabase is marked with annotation @ApplicationContext, why ?

2. In Code B, the parameter logDao of class LoggerLocalDataSource is injected, but the author doesn't add any annotation, why?

3. In Code C, I'm told the following content, why isn't the parameter activity of class AppNavigatorImpl added any annotation? and you know ApplicationContext is predefined binding too, but the author add annotation @ApplicationContext in fun provideDatabase in Code A.

Because an AppNavigator instance is provided in the Activity container , FragmentActivity is already available as a predefined binding.

Code A

@InstallIn(SingletonComponent::class)
@Module
object DatabaseModule {

    @Provides
    @Singleton
    fun provideDatabase(@ApplicationContext appContext: Context): AppDatabase {
        return Room.databaseBuilder(
            appContext,
            AppDatabase::class.java,
            "logging.db"
        ).build()
    }

    @Provides
    fun provideLogDao(database: AppDatabase): LogDao {
        return database.logDao()
    }
}

Code B

class LoggerLocalDataSource @Inject constructor(private val logDao: LogDao) : LoggerDataSource {
   ...
}

Code C

class AppNavigatorImpl @Inject constructor(private val activity: FragmentActivity) : AppNavigator {
   ...
}

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
    @Inject lateinit var navigator: AppNavigator
    ...
}