Step 1: Tocolysis means relaxation of the uterus (decrease in uterine tone). The volatile halogenated inhalational anaesthetics relax smooth muscle, including uterine smooth muscle, in a dose dependent fashion.
Step 2: Halothane, enflurane and isoflurane all produce a dose dependent fall in uterine tone. They reduce both the frequency of uterine contractions and the interval between them, so all three are tocolytic.
Step 3: Since each of the three agents listed has this effect, the correct answer is All the above. This property is why deep volatile anaesthesia can be used for uterine relaxation during procedures like manual removal of a retained placenta.