Duration of trusts may be altered by which of the following provisions?

The correct choice indicates that spendthrift provisions can impact the duration of trusts by controlling the beneficiary's access to the trust assets. Spendthrift provisions safeguard trust assets from the creditors of the beneficiary, ensuring that the assets are protected until specific conditions are met. However, these provisions do not directly alter the trust's duration; they primarily focus on the distribution of the assets to the beneficiary.

In examining the context of altering a trust's duration, termination provisions are more pertinent as they specifically dictate when a trust may end, either upon the fulfillment of certain conditions or when specific events occur. Revocation clauses grant the trustor the right to revoke the trust entirely, which would also effectively determine the trust's lifespan. Limitations provisions generally set conditions or restrictions on the trustee’s additional powers but do not inherently extend or shorten the trust’s duration.

Therefore, while spendthrift provisions play a protective role in managing how trust assets are accessed by beneficiaries, they do not directly alter the duration of the trust in the same manner as the other listed provisions.