Question

as british scientist peter whibberley has observed, \the earth is not a very good timekeeper.\ earths slightly irregular rotation rate means that measurements of time must be periodically adjusted. specifically, an extra \leap second\ (the 86,401st second of the day) is ______ time based on the planets rotation lags a full nine - tenths of a second behind time kept by precise atomic clocks. which choice completes the text so that it conforms to the conventions of standard english? choose 1 answer: a added, whenever b added; whenever c added. whenever d added whenever

Explanation:

• Option A: A comma is used to separate the main clause "an extra 'leap second' (the 86,401st second of the day) is added" and the subordinate clause "whenever time based on the planet's rotation lags a full nine - tenths of a second behind time kept by precise atomic clocks". This is correct punctuation for a complex sentence.
• Option B: A semicolon is used to separate independent clauses. Here, "whenever..." is a subordinate clause, not an independent clause, so a semicolon is incorrect.
• Option C: A period would create two separate sentences. But the second part "Whenever time based on the planet's rotation lags..." is a subordinate clause and cannot stand alone as a sentence.
• Option D: Without any punctuation, it makes the sentence hard to read and does not properly separate the main and subordinate clauses.

Answer:

A. added, whenever