Captain Jirk reports to headquarters that he left the planet Senesca 1.88 × 104 seconds earlier. Headquarters sends back the message: "Was that spaceship proper time?" It will be spaceship proper time if it was
◦ measured by one clock fixed at one spot on Senesca.
◦ measured by one clock fixed at one spot on the spaceship.
◦ measured by a clock on Senesca at departure and by a clock on the spaceship when reporting.
◦ measured by a clock on the spaceship when departing and by a clock on Senesca when reporting.
◦ calculated by dividing the distance from Senesca according to Senesca by the speed of the spaceship.
measured by one clock fixed at one spot on the spaceship.