A standard Argo ﬂoat, a type of autonomous robot, measures temperature and salinity in the upper regions of ice-free
oceans. More advanced ﬂoats can measure a wider range of ______ and monitor seasonal ice zones.
variables: travel to greater depths
variables, travel to greater depths,
variables travel to greater depths,
variables, travel to greater depths;
Choice B is the best answer. The convention being tested is the punctuation of items in a series. The comma after
“variables” is used conventionally to separate the ﬁrst and second items in the series, and the comma after “depths” is used
conventionally to separate the second and third items.
Choice A is incorrect because a colon can’t be used in this way to separate items in a simple series. Choice C is incorrect
because a comma is needed after “variables” to separate the ﬁrst and second items in the series. Choice D is incorrect
because a semicolon can’t be used in this way to separate items in a simple series.