Step 1: Understand the meaning of a regulatory institution.
A regulatory institution is an authority established by the government to regulate, supervise, monitor, and control the functioning of a particular sector or industry.
These institutions ensure transparency, fair practices, consumer protection, and efficient functioning of markets and public utilities.
Regulatory bodies generally frame rules, issue guidelines, monitor compliance, and sometimes impose penalties for violations.
Step 2: Analyze option (A) --- SEBI.
The Securities and Exchange Board of India (SEBI) is the regulator of India’s securities and capital markets.
It regulates stock exchanges, listed companies, mutual funds, brokers, and other market intermediaries.
SEBI protects investors’ interests and promotes the orderly development of the securities market.
Since SEBI performs regulatory and supervisory functions, it is a regulatory institution.
Hence, option (A) is correct.
Step 3: Analyze option (B) --- IRDAI.
The Insurance Regulatory and Development Authority of India (IRDAI) regulates the insurance sector in India.
It supervises insurance companies, protects policyholders’ interests, and promotes the orderly growth of the insurance industry.
IRDAI also grants licenses to insurance companies and frames regulatory norms.
Therefore, IRDAI is a regulatory institution.
Hence, option (B) is correct.
Step 4: Analyze option (C) --- SIDBI.
The Small Industries Development Bank of India (SIDBI) is primarily a development financial institution.
Its main objective is to provide financial assistance and support for the promotion and development of micro, small, and medium enterprises (MSMEs).
Although SIDBI supports industrial growth and financing, it does not function as a sectoral regulator.
It does not regulate or supervise industries in the way regulatory authorities do.
Hence, option (C) is incorrect.
Step 5: Analyze option (D) --- CERC.
The Central Electricity Regulatory Commission (CERC) regulates the electricity sector in India at the central level.
It determines electricity tariffs, regulates interstate transmission of electricity, and promotes efficiency and competition in the power sector.
CERC performs statutory regulatory functions under the Electricity Act.
Therefore, CERC is a regulatory institution.
Hence, option (D) is correct.
Step 6: Final conclusion.
Among the given institutions, SEBI, IRDAI, and CERC are regulatory institutions, while SIDBI is a development financial institution rather than a regulator.
Therefore, the correct answer is
\[
\boxed{(A),\ (B)\text{ and }(D)}
\]