Olivia owned a tract of land bordered on the north by Green Road and on the south by Brown Road. In 1996, Olivia built a house on the north half of the property which she called Greenacre. To reach the house, she sometimes used the front driveway leading north out to Green Road, but after heavy snows or heavy rains, Green Road was accessible only with a four-wheel-drive vehicle. Therefore, she often used ''the back way''a dirt track going over the southern half of the property, which she called Brownacre, leading to Brown Road. In 2006, Olivia sold Greenacre to Andrew and she built and moved into a house on Brownacre. Although the deed said nothing about an easement over Brownacre, Andrew frequently used the dirt track to reach Brown Road, which was a quicker way to reach his workplace. Olivia often saw him and would wave hello. In 2014, a mudslide closed Green Road, and county officials notified Andrew that the damage to the road was severe and might not be repaired for years. Thereafter, Andrew exclusively used the dirt track over Brownacre for ingress and egress. In 2016, Olivia sold Brownacre to Betsy. Soon thereafter, Betsy put up a locked gate across the dirt track and has forbidden Andrew to use it. In this jurisdiction, the statute of limitations for prescription is 10 years. Which of the following is Andrew's best theory for an easement over Brownacre?

(A) Estoppel

(B) Implied by necessity

(C) Prescription

(D) Implied by prior use