(from A Short History of Astronomy by Arthur Berry, 1910) Read the passage carefully and then choose the correct answer.

We have already spoken... of the lunar month as the period during which the moon returns to the same position with respect to the sun; more precisely this period (about 29 ½ days) is spoken of as a lunation or synodic month: as, however, the sun moves eastward on the celestial sphere like the moon but more slowly, the moon returns to the same position with respect to the stars in a somewhat shorter time; this period (about 27 days 8 hours) is known as the sidereal month. Again, the moon's path on the celestial sphere is slightly inclined to the ecliptic, and may be regarded approximately as a great circle cutting the ecliptic in two nodes..."

Which of the following is an example of a signal word?
stars
period
lunation
more