A standard Argo float, a type of autonomous robot, measures temperature and salinity in the upper regions of ice-free oceans....

Let's begin by understanding the meaning of this sentence. We'll use our understanding of pause points and segment the sentence as shown - understanding and assimilating the meaning of each segment bit by bit!

Sentence Structure

• 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 variables (?) travel to greater depths (?) and monitor seasonal ice zones.

Understanding the Meaning

The first sentence gives us context:

• 'A standard Argo float, a type of autonomous robot'
  • tells us what an Argo float is – it's a robot

• 'measures temperature and salinity in the upper regions of ice-free oceans'
  • tells us what standard floats do – they measure things in the upper parts of oceans

Now the second sentence contrasts this with more advanced floats:

• 'More advanced floats can measure a wider range of variables...'
  • So these fancier floats can measure more types of things

This is where we have the blank. Let's look at the choices:

• The punctuation varies around "travel to greater depths"

To see what works here, let's read the rest of the sentence and understand what it's saying!

The sentence continues: '...and monitor seasonal ice zones.'

Now let's understand what this complete sentence is telling us about what more advanced floats can do:

• 'can measure a wider range of variables'
  • First action – they measure more types of things

• 'travel to greater depths'
  • Second action – they go deeper in the ocean

• 'and monitor seasonal ice zones'
  • Third action – they can work in areas with seasonal ice

What do we notice about the structure here?

• We have three parallel actions that all share the helping verb "can":
  • can measure
  • can travel
  • and can monitor

• These are three items in a series – three things the advanced floats can do

• When we have a series of three or more items, we separate them with commas:
  • First item, second item, and third item

So we need: variables, travel to greater depths,

The correct answer is Choice B.

Grammar Concept Applied

Using Commas to Separate Items in a Series with Shared Helper Verbs

When you have three or more parallel actions that share a helping verb (like "can," "will," "should," etc.), you need to separate them with commas, even though the helping verb isn't repeated:

Pattern:

• Subject + helping verb + action 1, action 2, and action 3

Example 1:

• The new software can analyze data, generate reports, and send alerts.
• can analyze (action 1)
• [can] generate (action 2)
• and [can] send (action 3)

Example 2:

• Students should review the material, complete the practice problems, and prepare questions for class.
• should review (action 1)
• [should] complete (action 2)
• and [should] prepare (action 3)

In our question:

• More advanced floats can measure a wider range of variables, travel to greater depths, and monitor seasonal ice zones.
• can measure (action 1)
• [can] travel (action 2)
• and [can] monitor (action 3)

The commas clarify that these are three separate, parallel actions that the floats can perform.