A punctuation question tests how a joining word connects sentence parts. Split at that word and test whether each side can stand alone with a subject and a main verb that says what the subject does or is. A comma plus a joining word connects full sentences; no comma separates two verbs sharing one subject. A semicolon joins full sentences without a joining word; a colon follows a full sentence and introduces an explanation. Sentence structure decides the punctuation, not pauses.
Hints
- Hint 1
Look for the subject and main verb on each side of the blank. Who lost contact, and who was able to confirm the landing?
- Hint 2
Read each side without but and ask whether it can stand alone. Then use that result to decide how the joining word connects the parts.
Step-by-step
Split and test the join
Step 1Test the first part
Split before but, the joining word in every choice, and test the words on each side as separate sentences. Before the blank, the spacecraft lost contact with needs only the common words mission control to finish the thought. Can that first part stand alone? It has the subject spacecraft and main verb lost, so it is a full sentence. The opening phrase tells us when contact was lost without making the first part depend on what comes next.
- Step 2
Find the second subject and verb
What about the words after but? engineers were still able to confirm a successful landing has the subject engineers and main verb were, while the final phrase tells us how they confirmed it. The second part can stand alone too, so but connects two full sentences with separate subjects, not two verbs sharing one subject. What does but tell us about their link? It shows that the engineers could confirm the landing even though the spacecraft lost contact.
- Step 3
Give the joining word its punctuation
Between two full sentences, a comma and a joining word work as a pair. mission control but leaves out the comma, while mission control; but uses a semicolon, which normally joins full sentences without a joining word. A colon would introduce an explanation of the first part, so mission control: but doesn't fit: the spacecraft lost contact, yet the engineers were still able to confirm a successful landing. mission control, but gives the joining word its comma, which these two full sentences need. Choice B.