Question from the Angular test

import { Calendar } from './calendar.component';

@NgModule({
    declarations: [Calendar]
})
export class CommonModule { }

import { Calendar } from './calendar.component';

@NgModule({
    declarations: [Calendar],
    exports: [Calendar]
})
export class CommonModule { }

import { Calendar } from './calendar.component';

@NgModule({
    exports: [Calendar]
})
export class CommonModule { }

import { Calendar } from './calendar.component';

@NgModule({
    declarations: [Calendar],
    providers: [Calendar]
})
export class CommonModule { }