In Question Q$1,$ the decryption key of homomorphic encryption is required when decrypting the ciphertexts downloaded from the cloud. If you lost your decryption key, you would lose all of your date stored in the cloud.

In order to be able to recover your decryption key, suppose that you decide to use Shamir$$s secret sharing scheme. Shamir's Secret Sharing is an approach to share secret, where a secret is divided into parts, giving each participant its own unique part. To reconstruct the original secret, a minimum number of parts is required.

Following Shamir$$s secret sharing scheme, suppose that you divide your decryption key into $4$ parts, storing $4$ parts in four different clouds as shown in Figure $2.$ If you lost your decryption key, you should be able to recover it with any $3$ parts.