Introduction:
Rylands v Fletcher is a landmark case in the field of tort law that established the principle of strict liability. The case involved the escape of water from a reservoir owned by the defendant, which caused damage to the claimant's property. The court's decision in this case laid down the rule of strict liability.

Explanation:
Strict liability is a legal principle that holds a person or organization responsible for their actions or omissions regardless of their intent or fault. In other words, it imposes liability on the defendant based solely on the fact that they engaged in a particular activity or owned a particular property, regardless of whether they were negligent or at fault.

Key Points:
Here are some key points that explain why the correct answer is option 'A' (strict liability):

1. The Facts of the Case:
In the case of Rylands v Fletcher, the defendant owned a reservoir on their land. The reservoir was constructed to supply water to their mill. However, the defendant had employed independent contractors to build the reservoir, and during the construction, they discovered several old shafts and passages beneath the land. Despite knowing about these potential risks, the defendant proceeded with the construction without taking adequate measures to prevent the escape of water.

2. Escape of Water:
After the reservoir was filled, the water escaped through the shafts and passages underground and caused damage to the claimant's property. The claimant sued the defendant, alleging negligence and claiming compensation for the damage caused.

3. The Court's Decision:
The court held that the defendant was liable for the damage caused, even though they were not negligent. The key principle established in this case was that if a person brings or accumulates on their land something that is likely to cause harm if it escapes, and it does escape and causes damage, then they are strictly liable for that harm.

4. Strict Liability:
The rule of strict liability means that the defendant will be held liable for the consequences of their actions or omissions, regardless of their intent or fault. This is different from fault liability, where the defendant's negligence or fault needs to be proven for them to be held liable.

Conclusion:
In conclusion, Rylands v Fletcher established the principle of strict liability in tort law. The defendant was held liable for the damage caused by the escape of water from their reservoir, even though they were not negligent. This case marked a significant development in tort law by introducing the concept of strict liability, which imposes liability on a defendant based on their actions or ownership of property, rather than their fault or negligence.