A punctuation question with a long description tests whether the words after the blank can stand alone. Cover what follows to test the first part, then read to the end for a main verb in the second. A period or semicolon separates complete sentences; a colon introduces a list or explanation after a complete sentence; a comma attaches added details. An -ing word needs a helper, such as is, to be a main verb.
Hints
- Hint 1
Supply inventions, which appears in every option, and cover everything after it. Test whether the opening can stand alone.
- Hint 2
Look at the verb forms after the blank. Could fascinating or promising be a main verb without a helper?
- Hint 3
Decide how the two parts are related: how does the machine description connect to what comes before the blank?
Step-by-step
Test both sides of the blank
Step 1Check the opening
Read up to inventions, which every option includes. The passage's visitors marveled gives us a subject and main verb, and at cutting-edge agricultural leads into what they marveled at. Can that opening stand alone? Yes, so the first part is a full sentence, and we can now test what follows.
- Step 2
Find a main verb after the blank
Where is the main verb for the demonstration? In fascinating crowds, fascinating describes the demonstration; an -ing word needs a helper such as was to be a main verb. In its rhythmic pistons promising, promising has no helper such as were, even though there's a noun before it. Finally, increased efficiency and reduced labor names the benefits rather than adding a main verb. The long description can't stand alone as a sentence.
- Step 3
Test the period and semicolon
Can we end the sentence here? A period or semicolon must be followed by a full sentence. The version with a period and the version with a semicolon would leave everything from demonstration of a portable milking machine onward as a fragment, a group of words that can't stand alone.
- Step 4
Introduce the example
How does the demonstration of a portable milking machine connect to the opening? It gives a specific example of what visitors marveled at, rather than renaming the inventions themselves. The comma in inventions, the would treat the demonstration as a renaming. A colon introduces an example after a full sentence, so inventions: the makes the needed link. Choice B.