Red Hot Roots #5

The outer boundary of something is called the

(a)  

• periphery
• circulatory
• period

To go around or bypass is to ​ ​ (a)  

• circumvent
• periodic
• periscope

​ (a)   ​ means a revolving; a journey around, a route​

• circumstance
• circuit
• periphery

An instrument for seeing around things is called a ​ (a)  

• periscope
• period
• circumnavigate

​ (a)   means to sail around

• circumnavigate
• circumvent
• periscope

The interval between certain happenings is called a ​ (a)  

• period
• periodic
• circumstance

​ (a)   means going in a circuit; circular

• circulatory
• circumnavigate
• periodic

The ​ (a)   is the condition surrounding or related to an event

• circumstance
• periphery
• circuit

​ (a)   means happening at regular intervals; happening from time to time

• periodic
• periscope
• circulatory

What is the prefix meaning "around?"