Final answer:
The appropriate form of the verb ser in the given sentence is sea.
Step-by-step explanation:
The appropriate form of the verb ser in the given sentence is sea.
The conjugation of the verb ser in the present subjunctive is sea, which is used after expressions of doubt, fear, uncertainty, or desire.
For example, in the sentence given, the expression of fear (tengo miedo de que) triggers the use of the subjunctive form sea.
Learn more about Conjugation of the verb ser in Spanish