Multi-choice problem: Continue writing the next sentence in this paragraph:

How to test fluorescent bulbs
Look for dark areas at the base of the bulb.
When bulbs age and have been used for a long time, brown spots will appear. If darkness begins to form at the ends of the tube, the bulb may be near its end.

Available choices:
(a). Look for the phosphorescent lining along the outside of each bulb at the base. This is called " phosphorescent coating.;
(b). While they may still light, they are wearing out and will die soon. If the darkness only forms on one end of a tube light, flip the tube so the darkened end is on the opposite side of the fixture.;
(c). Identify or remove a covered bulb when it is on display. Fluorescent bulbs that are attached to battery fixtures tend to have a covering or sticker on them that attaches the light to the light bulb.;
(d). Examine the cap carefully and look for rings. While fluorescent bulbs are not inherently dangerous, they can emit uva radiation that is dangerous to humans if ingested.;
(b).