Introduction:
In the field of commerce, public sector undertakings (PSUs) play a crucial role in the economic development of a country. PSUs are government-owned corporations or entities that operate in various sectors to provide essential goods and services to the public. They are established and governed by the government to fulfill specific social and economic objectives.

Explanation:
The given options are:
a) Partnership
b) Departmental undertaking
c) Government companies
d) Statutory corporation

Partnership:
Partnership refers to a business structure where two or more individuals come together to carry out a business with a common objective. A partnership is not a public sector undertaking as it is formed by private individuals and does not have any government ownership or control. Therefore, option 'A' is the correct answer as it does not fall under the category of public sector undertakings.

Departmental undertaking:
A departmental undertaking refers to a business unit or enterprise that is directly owned and operated by the government department. These undertakings are established to carry out specific activities or functions of the government. They are fully funded by the government and operate under its control and direction. Departmental undertakings are considered as public sector undertakings.

Government companies:
Government companies are entities that are established and owned by the government to engage in various commercial activities. These companies have a separate legal identity and operate under the Companies Act. The majority of the shares in these companies are held by the government, either directly or through other government-owned entities. Government companies are an example of public sector undertakings.

Statutory corporation:
Statutory corporations are autonomous bodies that are created by an Act of Parliament or State Legislature. These corporations are established to perform specific functions or provide essential services to the public. They have their own legal identity and operate independently of the government. Statutory corporations are considered as public sector undertakings.

Conclusion:
In summary, out of the given options, partnership is not a public sector undertaking. Public sector undertakings are government-owned corporations or entities that operate in various sectors to provide essential goods and services to the public. They are established and governed by the government to fulfill specific social and economic objectives.