These questions are from the OG 10. These are the OA with official explanations:

1) A

Choice A, the best answer, preserves grammatical parallelism while allowing for logical expression of temporal
relationships; A employs the parallel participial phrases spawned... and extending ... to modify filigree. Other
choices present different grammatical constructions that are not participial modifiers and thus not parallel to
spawned: extends in B is a present-tense verb; it extended in D begins a new clause; and is extending in E
ungrammatically introduces a new predicate. In C, extended is nonparallel if it is assumed to be a past tense
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verb form; if it is assumed to be a past participle, it illogically states, as does D, that the filigree extended only in
the past.


2) B

At issue is the need for logical and formal parallelism in a coordinate series. B, the best choice, clearly and
correctly uses parallel noun phrases to list three effects of a drop in oil prices: a lowering of..., a rally in ..., and
a weakening of.... In place of the correct lower before/ears, choice A uses an incorrect participial adjective,
lowering, that could cause confusion by seeming at first to function as a verb. A also violates parallelism. In C
and D, the use of along with confuses meaning by making fears about inflation an independent effect, not an
object of lowering. D and E violate parallelism by substituting an awkward gerund clause for the first noun
phrase.


3) C

A correct sentence must maintain parallel structure. In choice A, the three-part series (to diagnose ...,
deciding,... or other purposes ...) lacks parallelism. C, the best choice, replaces A's third element with/or such
purposes as; this phrase functions as a stem for the other two elements, which are recast as two parallel
phrases--diagnosing ... or deciding .... Thus, choice C not only manages the parallel structure but avoids the
less effective other purposes such as these at the end of choice A. Choice E uses faulty parallel structure (to
be used..., deciding ..., or the like). In B and D, which and the use of which introduce sentence elements that
lack antecedents or reference. In addition, D is wordy.