Write the next sentence in the following story.

How to care for a sandfish skink 
Get an appropriately sized terrarium. 
Growing to an average of only 6 inches long, sandfish skinks take up little space in the reptile world. For a single adult skink, use a 10-gallon tank.

Pick your answer from:
(a). Add an extra 7 gallons per extra skink. Use a horizontal tank to house them for they don't tend to climb much.;
(b). Once it grows, you'll need an adult tank and 10 gallon tank. The terrarium needs to have at least 4 gallons of water per gallon, which is enough water for the two skinks.;
(c). With larger brine tanks, you may only need 15-20 gallons of space. Young bucks can actually live in another 15 gallon aquarium, with six larger tanks surrounding it.;
(d). It is important to accommodate one skink and one adult. The tank should have spaces that are suited to the reptile's size.;. The answer should be
(a).