virtual 既有“实质的”（Existing or resulting in essence or effect though not in actual fact, form, or name:）又有“虚的”（Existing in the mind, especially as a product of the imagination. Used in literary criticism of text.）意思，考试的时候如果遇到，要怎么判断到底是哪个意思？
还有 ravel 这个词，也类似，既有纠缠的意思，又有解开的意思
举例来说：36套里面的这篇文章：
The essential condition for the decay of the vacuum is the presence of an intense electric field. As a result of the decay of the vacuum, the space permeated by such a field can be said to acquire an electric charge, and it can be called a charged vacuum. The particles that materialize in the space make the charge manifest. An electric field of sufficient intensity to create a charged vacuum is likely to be found in only one place: in the immediate vicinity of a superheavy atomic nucleus, one with about twice as many protons as the heaviest natural nuclei known. A nucleus that large cannot be stable, but it might be possible to assemble one next to a vacuum for long enough to observe the decay of the vacuum
2. The author‘s assertions concerning the conditions
that lead to the decay of the vacuum would be
most weakened if which of the following occurred?
(A) Scientists created an electric field next to a
vacuum, but found that the electric field was
not intense enough to create a charged
vacuum.
(B) Scientists assembled a superheavy atomic
nucleus next to a vacuum, but found that no
virtual particles were created in the vacuum‘s
region of space.
(C) Scientists assembled a superheavy atomic
nucleus next to a vacuum, but found that
they could not then detect any real particles
in the vacuum‘s region of space.
(D)Scientists introduced a virtual electron and a
virtual positron into a vacuum‘s region of
space, but found that the vacuum did not
then fluctuate.
(E) Scientists introduced a real electron and a real
positron into a vacuum‘s region of space, but
found that the total energy of the space
increased by the energy equivalent of the
mass of the particles