A punctuation question with and tests whether the words it joins can each stand alone. Split at the joining word, then read each side to its end. If a side opens by saying when something happens, look for a subject and verb after it. A comma with and joins full sentences, while no comma joins two verbs that share a subject. A semicolon normally joins full sentences without a joining word, and a colon introduces words that explain a full sentence.
Hints
- Hint 1
Split after and and test each side as a sentence. Who discovered something on the first side, and what's the verb?
- Hint 2
Read past the part beginning with when and continue to the end. Does that whole side have its own subject and main verb, or does it still leave you waiting for a complete thought?
Step-by-step
Split and read to the end
Step 1Test the first side
Split after and, which appears in every choice, to see whether it joins two full sentences. Can the first side stand alone? Caroline Herschel discovered several ends with comets, giving us a subject, Caroline Herschel, and a main verb, discovered, which tells what she did. The opening phrase describes how she worked without making the sentence depend on what follows, so the first side can stand alone.
- Step 2
Read to the end of the second side
The right side begins with when her brother William was appointed royal astronomer, which says when something happened. Can those words stand alone? No, because when leaves us waiting to hear what Caroline did at that time. But read past the comma to she continued to assist him: she is the subject, and continued is the main verb. The whole right side can stand alone, because the opening when part leads into that complete thought; the remaining words tell us she also pursued her own research.
- Step 3
Choose the mark that works with the joining word
Which mark works with the joining word and? A comma and and work as a pair between full sentences, so comets and lacks the comma and comets; and uses a semicolon where this join calls for a comma. The colon in comets: and would need the second side to explain the first, but Caroline's later work with William is a new event rather than an explanation of her discovery. The version with comets, and has the needed comma. Choice B.