OG says : This sentence 1 (oa c)explains how people void toll charges on their home phones and this purpose is best clarified by using preposition by to connect the phrase can avoid.... with the explanatory using their mobile phones..
However the sentence 2 (OA E) is with similar structure but without by. Thus can someone help me out when to exclude the preposition before ing phrase? .
Furthermore, Og says at a time which in sentence 1 is confusing because it seems to suggest a time other than at night or on weekend. Can someone elaborate what it means?
1.As the cost of wireless service has steadily dropped over the last year and as mobile phones have become increasingly common, many people are finding that they can avoid toll charges on their home phones, using their mobile phones for making long-distance calls at night or on weekends, at a time which many wireless companies provide unlimited airtime for a small monthly fee
a) same as above
b) phones, instead using mobile phones to make long-distance calls during the night of weekends, during which
c) phones by using their mobile phones to make long-distance calls at night or on weekends, when
d) phones using mobile phones for making long-distance calls during the night or weekends, when
e) phones when using their mobile phones to make long-distance calls at night or on weekends, a time which.
2.Hundreds of species of fish generate and discharge electric currents, in bursts or as steady electric fields around their bodies, using their power either to find and attack prey, to defend themselves, or also for communicating and navigating.
(A) either to find and attack prey, to defend themselves, or also for communicating and navigating
(B) either for finding and attacking prey, defend themselves, or for communication and navigation
(C) to find and attack prey, for defense, or communication and navigation
(D) for finding and attacking prey, to defend themselves, or also for communication and navigation
(E) to find and attack prey, to defend themselves, or to communicate and navigate
However the sentence 2 (OA E) is with similar structure but without by. Thus can someone help me out when to exclude the preposition before ing phrase? .
Furthermore, Og says at a time which in sentence 1 is confusing because it seems to suggest a time other than at night or on weekend. Can someone elaborate what it means?
1.As the cost of wireless service has steadily dropped over the last year and as mobile phones have become increasingly common, many people are finding that they can avoid toll charges on their home phones, using their mobile phones for making long-distance calls at night or on weekends, at a time which many wireless companies provide unlimited airtime for a small monthly fee
a) same as above
b) phones, instead using mobile phones to make long-distance calls during the night of weekends, during which
c) phones by using their mobile phones to make long-distance calls at night or on weekends, when
d) phones using mobile phones for making long-distance calls during the night or weekends, when
e) phones when using their mobile phones to make long-distance calls at night or on weekends, a time which.
2.Hundreds of species of fish generate and discharge electric currents, in bursts or as steady electric fields around their bodies, using their power either to find and attack prey, to defend themselves, or also for communicating and navigating.
(A) either to find and attack prey, to defend themselves, or also for communicating and navigating
(B) either for finding and attacking prey, defend themselves, or for communication and navigation
(C) to find and attack prey, for defense, or communication and navigation
(D) for finding and attacking prey, to defend themselves, or also for communication and navigation
(E) to find and attack prey, to defend themselves, or to communicate and navigate
