A question without proper answer

[Zishuli]

Here is a question in Test # TOEIC/ M197:

9. adv. either

(a) also; too; as well
(b) at an angle; obliquely; in a slanting direction
(c) without pleasure or happiness; wretchedly; poorly
(d) progressively

I think none of these options can be accepted, even though the given answer is (a) ' also; too; as well'.

[Gray]

Either:

After a negative statement used as an intensive meaning something like 'likewise' or 'also'

Example:

I don't know either.
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First lesson - English, not english. I, not i. ~A student of English

[Zishuli]