390.3. If there are not enough options to make legal choices for a Triggered Ability that has been put on the chain, remove it from the Chain now. It ceases to be a Pending Item but never becomes a Chain Item.
390.3.a. This is not an Ability being countered.
390.3.b. If there are legal options to choose, the ability’s controller must choose them. They may not decline this stage of playing a Trigger.