(fill the gaps with the simple present or simple future form of the verbs in brackets. the sun (continue) much as it is today until it (enter) its red giant phase in 4 to 5 billion years. then, the core (grow) smaller and hotter until it finally (finish) burning the fuel in its nuclear core. when this (occur) the core (become) so dense that helium fusion will begin. when the helium atoms (collide) they (form) carbon (from 3 helium atoms) and oxygen (from 4 helium atoms). when this process (begin) the sun (produce) enormous amounts of energy. the sun (grow) larger as this energy (increase). it (be) over a hundred times its present size by the time it (stop) growing. this is why we use the term red giant. as the sun (expand) it is probable that it (absorb) the earth. when the sun (use) up all its energy, it (become) a small white dwarf, and (not make) any more energy. after a few billion years, when it (be) completely cool, it (be) just a cold dark object.

The Sun (will continue) much as it is today until it (enters) its red giant phase in 4 to 5 billion years. Then, the core (will grow) smaller and hotter until it finally (finishes) burning the fuel in its nuclear core. When this (occurs) the core (will become) so dense that helium fusion will begin. When the helium atoms (will collide), they (will form) carbon from 3 helium atoms and oxygen from 4 helium atoms. When this process (begins) the Sun (will produce) enormous amounts of energy. The Sun (will grow) larger as this energy (increases). It (will be) over a hundred times its present size by the time it (stops) growing. This is why we use the term red giant. As the Sun (expands) it is probable that it (will absorb) the Earth. When the Sun (uses) up all its energy, it (will become) a small white dwarf, and (will not make) any more energy. After a few billion years, when it (is) completely cool, it (will be) just a cold dark object.