Name some sources of direct current.

Hint: To get the right answer you need to know that the current is charged in coulomb flowing per second. Direct current is that current which is not changing or alternating. Direct current comes from the sources which produce a constant voltage at the two terminals of the circuit. Knowing these things you will find the sources which produce direct current.

Complete step-by-step answer
Current =$\dfrac{{{\text{charge(coulomb)}}}}{{{\text{time(second)}}}}$.
Direct current - Direct current is the electrical charge of one-directional or one-way flow. Electrochemical cells are a prime example of DC power. Direct current can flow through a conductor, such as a wire, but it can also flow through semiconductors, insulators, or even through the vacuum, such as the electron or ion beams.
The current which is not direct is alternating current.
And the definition of alternating current is,
Alternating current - Alternating current ( AC) is an electrical current that periodically reverses direction and changes its magnitude continuously in contrast to the direct current (DC) which flows only in one direction.
From the definition of direct current above we come to know that,
The sources of direct current are,
1) Generally, All types of Batteries produce direct current.
2) We get Power supplies current as direct current.
3) One of the best sources of energy that is solar energy produces direct current.

Note: Direct current does not vary itself as the alternating current does. But we can produce direct current with alternating current also with the help of some suitable means. The direct current can be converted from the alternating current supply by means of a rectifier containing either electronic (usually) or electromechanical (historically) elements that allow the current to flow only in one direction. Direct current can be converted to the alternating current through an inverter.