The NOR gate is logically equivalent to an OR gate followed by
(A) an inverter
(B) a NOR gate
(C) a NAND gate
(D) all of these

Hint
Logic gates are the first basic form of any digital system. It is an electronic circuit which needs one or more than one input but the output of the logic gates is always one output. The relation between the input and the output is fully based on the types of logic gates.

Complete step by step answer
There are several types of the logic gates which perform several actions. The types of logic gates are AND gate, OR gate, NAND gate, NOR gate, EX-OR gate and some types are available. The above-mentioned logic gates are widely and frequently used logic gates. And the different types of logic gates are performing different types of functions. For example, AND gates are supplied with the two inputs in four stages, the output of the AND gate is a product of the two inputs of the four stages. Like that the OR gate performs, addition of the two inputs. The NAND gate is the opposite value of the AND gate and NOR gate is the opposite value of the OR gate.
Now, the OR gates inputs of $ A $ is $ 0 $ , $ 0 $ , $ 1 $ , $ 1 $ and the input of the $ B $ is $ 0 $ , $ 1 $ , $ 0 $ , $ 1 $. These two are the inputs of the OR gate, the output of the OR gate is the sum of the two inputs, $ 0 $ , $ 1 $ , $ 1 $ , $ 1 $ . Then the output of the NOR gate is $ 1 $ , $ 0 $ , $ 0 $ , $ 0 $. So, that the output of the NOR gate is the opposite value of the OR gate. So, the NOR gate is logically equivalent to an OR gate followed by an inverter. The inverter is the device which gets one input and gives one output, but the output is the opposite value of the input.
Hence, the option (A) is the correct answer.

Note
The NOR gate is equal to the combination of the OR gate and the inverter. Both are given the same output, but the efficient way is NOR gate because it is a single gate but the combination of the OR gate and an inverter is two gates, so NOR gate is more efficient.