Jawaban:

ON

1. The letter came on Monday

2. I will start the job on 5th of June

3. I promise I will be there on your birthday

4. They will be back on Christmas day.

IN

1. He was born in January

2. I think it was invented in 1992

3. We will be rich in the future

AT

1. The show starts at 3 o'clock PM

2. The breakfast is ready at sunrise

3. We will gather again at dinner time.

Penjelasan:

Preposisi ON biasanya dipakai ketika menyebutkan: hari (Senin , selasa dst), tanggal (1 Januari, 5 Mei dst), atau even-event/perayaan tertentu (Independence Day, Christmas, Birthday dll)

IN biasanya dipakai ketika menyebutkan: Bulan (Januari dst), Tahun/Abad, atau periode yang panjang seperti musim (in summer, in winter dst),

AT dipakai ketika menyebutkan titik waktu yang spesifik misalnya jam (at one o'clock), at breakfast (tepat pada waktu sarapan),