Fusion occurs in the of the sun, where the pressure and temperature are very high.
a. photosphere
b. core
c. chromosphere
d. solar wind

The answer is B)core..
The Sun gets its energy from its core. The high pressure and heat, which results in fusion, creates a very powerful energy. The fusion is created with the assistance of hydrogen nuclei, which fuse and create a product of helium

The radiation of the fire causes the saucepan to heat up. the conduction of the saucepan then to distribute the heat over the saucepan and to give heat to the water. the convection of the water distributing the heat within the water, till all the water is boiling