Answer:
a. hydrogen gas and add heat and pressure.
Step-by-step explanation:
Now, the complete question is:
In order to recreate the process of energy production that takes place in the Sun, scientists use
a. hydrogen gas and add heat and pressure.
b. helium gas and remove heat and pressure.
c. hydrogen gas, add heat, and remove pressure.
d. helium gas, remove heat, and add pressure.
To simulate the condition of sun, it has to be understood the basic process of energy generation in stars. It is done through nuclear fusion, in which due to heat and pressure, hydrogen gas nuclei combine to form helium, the energy produce in form of heat.
Now, it is obvious that heat is to be added rather than removed, so all options with heat removal are eliminated. Similarly, extreme pressure also results in fusion reaction, so pressure must be added instead of removal. So, there is only option "a", which is correct, because heat and pressure both are added in process.