Common brown rat is

The correct option is "Rattus norvegicus".

To understand why this is correct, we can look at the scientific classification of common rat species:
1. Rattus norvegicus: Commonly known as the brown rat, Norway rat, sewer rat, or wharf rat. It is one of the most well-known and common rat species globally.
2. Rattus rattus: Commonly known as the black rat, ship rat, or house rat.
3. Rattus meltada: Commonly known as the soft-furred field rat, native mainly to Asia.
4. Bandicota bengalensis: Commonly known as the lesser bandicoot rat or Indian mole-rat.

Therefore, the scientific name for the common brown rat is strictly Rattus norvegicus.