Q: You are given a paragraph, with numbered sentences, and a question. Write the numbers of the sentences needed to answer the given question. Separate multiple sentence numbers with a comma (", "). E.g. "1, 2" would be the correct response if Sent 1 and Sent 2 are needed to answer the given question (do not include sentences that contain no information that is necessary to answer the question). Sort the sentence numbers in an increasing order (i.e., '1, 2', instead of '2, 1'). Your answer should not contain anything than the sentence numbers separated by a comma (e.g. '1, 2, 3, 4'). The given question requires more than one sentence to answer. So, your answer must contain at least one comma (", ").
Paragraph- Sent 1: What if two children push a swing at the same time?
Sent 2: Would the swing go higher?
Sent 3: Yes, together their force would be more.
Sent 4: It is common for forces to be combined.
Sent 5: Most objects on Earth have at least two forces acting on them.
Sent 6: Do you know what one of them is?
Sent 7: Of course, that force is gravity.
Sent 8: How many forces do you have on you right now?
Sent 9: Gravity pulls you down toward the center of Earth.
Sent 10: Your legs exert a downward force.
Sent 11: They hold you up against the pull of gravity.
Sent 12: Consider the example in Figure 1.3.
Sent 13: A book is resting on a table.
Sent 14: Gravity pulls the book downward.
Sent 15: It has a force of 20 newtons.
Sent 16: At the same time, the table pushes the book upward.
Sent 17: Its force is also 20 newtons.
Sent 18: The table opposes the pull of gravity. 
Question: Which forces affect a book resting on a table?.
A:
14, 16.