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题库 / Prep2007E2-SC-135
Whereas high speeds generally cannot be achieved by ramjets without their initially being assisted by a rocket, a scramjet, or supersonic combustion ramjet, can attain high speeds by reducing airflow compression at the entrance of the engine and letting air pass through at supersonic speeds.
Whereas high speeds generally cannot be achieved by ramjets without their initially being assisted by
Whereas a ramjet generally cannot achieve high speeds without the initial assistance of
With ramjets, high speeds generally are not able to be achieved without initially being assisted by
Unlike with ramjets, generally unable to achieve high speeds without the initial assistance of
Although a ramjet generally does not have the capability of achieving high speeds without the initial assistance from
ability：sb&aposs ability to do sth或ability of sb/sth to do sth
capability to do不如ability to do简洁，但不可就此判错。
be able to do
be capable of doing
have ability to do ; ability of sb. to do
have capability to do doing ; capability of sb. to do doing
因为后面用的can，这里用can会更好：将复杂句子里能统一的地方尽量统一，以便于读者理解。
ability：sb&aposs ability to do sth或ability of sb/sth to do sth
capability to do不如ability to do简洁，但不可就此判错。
be able to do
be capable of doing
have ability to do ; ability of sb. to do
have capability to do doing ; capability of sb. to do doing
This is not a grammar issue. Just think about whether the ideas at hand are "bullet points", or "A and B", or "#1 and #2", or whatever.
E.g.,
(A) Ramjets do this.
(B) Scramjets do that.
These make sense as "A and B", or as "two bullet points". So, make them parallel.