Is the verb in the sentence in the active voice or the passive voice?

The dog dug a hole in the yard to bury its bone.

a. active voice

b. passive voice

a. active voice

Example of an active voice:

For years, visitors to Loch Ness in Scotland has spotted a so-called monster. Many witnesses has reported the large creature. Do lake monsters really exist? Scientists have questioned these reports. According to same Canadian scientists, temperature inversions may explain the sightings. A temperature inversion occurs when the temperature of a body of water is much lower than the temperature of the air above it. A scientist on Lake Winnipeg, Canada conducted experiments during a temperature invasion. Two photos of an ordinary stick floating on the lake were taken only three minutes apart. The bending, or refraction, of light caused by the inversion made the stick appear to be a strangely shaped "monster." Some scientists have accepted these photos as proof that the lake monsters are really ordinary objects that appear distorted because of temperature inversion.