Read the sentences. When bricking a building, masons must fit the bricks together. Sometimes, masons slice bricks in half for a better fit. Which is the best way to combine the sentences? When bricking a building, masons must fit the bricks together; sometimes they slice bricks in half for a better fit. When bricking a building: masons must fit the bricks together; sometimes they slice bricks in half for a better fit. When bricking a building, masons must fit the bricks together; Sometimes they slice bricks in half for a better fit.

The best way to combine the sentences is "When bricking a building, masons must fit the bricks together; Sometimes, they slice bricks in half for a better fit."

Explanation:

The best way to combine the sentences presents the use of commas and a semicolon.

The first comma follows the rule of "Use a comma after a dependent clause that starts a sentence", then "When bricking a building," is the depending clause.

The semicolon follows the rule "to link (in a single sentence) two independent clauses that are closely related in thought" both sentences are talking about the same process, then " ... the bricks together; Sometimes, they slice bricks ... " is the merge of the two sentences into one.

The second comma follows the rule "Use a comma after introductory adverbs". Sometimes is a frequency adverb, then "Sometimes, they ..."

When bricking a building, masons must fit the bricks together; sometimes they slice bricks in half for a better fit.

Explanation:

This sentence has the appropriate punctuation of the comma and the semicolon. Also, the sentence follows the rule of having a letter lowercase after a semicolon.