Hey,
Not an expert but taking my best shot:
1-)
'' These are machines that take room air and extract the nitrogen, producing greater than 90% pure oxygen. ''
Ans. Producing here is functioning as a verb modifier. As per the meaning, it does not seem to refer to the main subject i.e. machines, but rather seem to provide additional information regarding the effect of the prior clause.
2-)
The drug disrupted the mechanism in the body, causing a heart attack.
The drug disrupts the mechanism in the body, causing a heart attack.
Is it necessary to have the past tense in such sentences ? Because only past tense examples are given in gmat book. For example :
The engineer fixed the problem, earning a promotion or She slipped on the ice, breaking her ankle.Ans. The use of past-tense will depend on the meaning of the sentence. In case we want to refer to an action that started and ended in the past, it is apt to use past tense. However, in cases where we talk about
general habits, it is apt to use simple present tense.
3-) Our bodies can sweat, losing heat by evaporation.
Can this sentence be thought of in two ways? For example :
Our bodies can sweet and this ( our bodies can sweet ) cause lose heat by evaporation
Our bodies can sweet and (our bodies ) lose heat by evaporationAns. Yes, basis the meaning this sentence can be restructured.
However, in the first case, instead of using
"this (out bodies sweat)", we shall use "causing" i.e. a verb modifier since such a modifier details the effect of the act of sweating.
Hence, the new sentence could be:
Our bodies can sweet, causing loss of heat by evaporation. OR
Our bodies can sweet, losing heat by evaporation. (Preferred to the first version since Verb>Adjective>Noun)
In the second case, i.e., Our bodies can sweet and (our bodies ) lose heat by evaporation - the implied meaning is correct and parallelism remains intact. Hence, this is also a correct usage.
The right answer choice will depend on the sentence meaning. To get an understanding of the kind of meaning that the question expects, try using the original stem for building meaning-context.