That we arrived just then was lucky.

which kind of clause are the words in bold?

a.

adverb clause
b.

adjective clause
c.

noun clause

The words in bold are "that we arrived just then."

C) Noun clause.

Explanation: A noun clause is a dependent clause that acts as a noun. They begin with words such as how, that, what, whatever, when, where, whether, which, whichever, who, whoever, whom, whomever, and why. And they can act as subjects, direct objects, indirect objects, predicate nominatives, or objects of a preposition. In the given sentence, the phrase "that we arrived just then" is an example of a noun clause.

there is no poster. if you add a poster then we can answer.

the characters in string all have major secrets that they strive to avoid revealing throughout the play.