canal: a passage of water *that* boats can travel

[What is the part of speech of *that* in the phrase?]

4 answers

1. canal: a passage of water *that* boats can travel
[What is the part of speech of *that* in the phrase?]

2. Boats can travel a passage of water.
3. Boats can travel on a passage of water.
4. Boats can travel through a passage of water.
[Which one is grammatical of the three?]
I would not in English use that phrase, however, as it is, it connects two clauses, so conjunction .

My usage...
canal: a passage of water in which boats can travel.
4. through
Bob Pursley is right. The preposition "through" is the best one to use for this expression.

In any case, the word "that" (or "which") is a relative pronoun, introducing an adjective clause that modifies "water."
http://grammar.ccc.commnet.edu/grammar/pronouns1.htm#relative