No nuclear reactions occur in the interior of a white dwarf. its brilliance comes from stored heat. therefore, the fate of an isolated white dwarf is to slowly lose its stored energy and dim over a long period of time. however, if a white dwarf is a member of a binary-star system with specific properties, the white dwarf can become explosively active. label the components of such a binary-star system capable of producing a nova event.
a. mass-transfer stream
b. accretion disk
c. main-sequence or giant companion star
d. white dwarf

B. Accretion disk.

Explanation:

According to results from such experiments and its likes, it is known that for a white dwarf to become explosively active, the distance between the dwarf and the companion must be small enough that the white dwarf's gravitational field can pull matter away from the surface of the companion. Due to the rotation of the binary system, the matter flowing through the mass transfer stream from the companion star forms a flattened disk which is called an accretion disk which orbits around the white dwarf.

what are the options.

explanation:

can be answered using momentum.

momentum = p

p1= mass1 * velocity1

p1 = p2

therefore

p1 = 6kg * 4m/s

p1 = 24kgm/s

p2=m2 * v2

24 kgm/s = 7kg * v2

v2 = 24 kgm/s / 7kg

v2= 3.42 m/s