(_b_) But _what_ had become of them they knew not.

3. (_a_) These are the lines _which_ heaven-commanded Toil shows on
his deed.

(_b_) And since that time I thought it not amiss To judge _which_
were the best of all these three.

In sentences 1 (_a_), 2 (_a_) and 3 (_a_) the regular relative use is
seen; _who_ having the antecedent _gentleman_, _what_ having the
double use of pronoun and antecedent, _which_ having the antecedent
_lines_.

But in 1 (_b_), 2 (_b_), and 3 (_b_), there are two points of
difference from the others considered: first, no antecedent is
expressed, which would indicate that they are not relatives; second, a
question is disguised in each sentence, although each sentence as a
whole is declarative in form. Thus, 1 (_b_), if expanded, would be,
"Who stood behind? We knew," etc., showing that _who_ is plainly
interrogative. So in 2 (_b_), _what_ is interrogative, the full
expression being, "But what had become of them? They knew not."
Likewise with _which_ in 3 (_b_).

[Sidenote: _How to decide._]

In studying such sentences, (1) see whether there is an antecedent of
_who_ or _which_, and whether _what_ = _that_ + _which_ (if so, it is
a simple relative; if not, it is either an indefinite relative or an
interrogative pronoun); (2) see if the pronoun introduces an indirect
question (if it does, it is an interrogative; if not, it is an