Final answer:
The correct word to complete the sentence is 'advisable,' meaning that it's wise or recommended, especially regarding safety practices like wearing a helmet.
Step-by-step explanation:
The correct word to fill in the blank is 'advisable.' The sentence should read: It is not advisable for you to ride without a helmet. 'Advisable' means to be appropriate or wise, particularly in reference to an action that is recommended. The other options, 'advisible,' 'adviseable,' and 'adviseible' are incorrect and are not recognized spellings in the English language. When it comes to safety, especially in activities such as riding a bicycle or motorcycle, wearing a helmet is always advisable to protect oneself from potential injuries.