Which of the following sentences with introductory elements use correct punctuation? Check all that apply.

a) Since he had finished his presentation outline he started designing presentation visuals.

b) Introducing speakers before presentations, is always a challenge.

c) On my desk between the paperweight and the clock, you'll find the form you need.

d) At the request of the governor's office, the economic science lab produced various forecasting models.

e) Between sessions the conference participants visited the cafeteria.

f) When the account manager returns from lunch, we'll double-check the meeting time.

d) At the request of the governor's office, the economic science lab produced various forecasting models

f) When the account manager returns from lunch, we'll double-check the meeting time.

Explanation:

In most of the cases, when a sentence begins with an introductory element, we should put a comma after it. This is the case with sentences a), c), d) e) and f). Sentence a) lacks a comma after the introductory clause - the correct version of this sentence should be - Since he had finished his presentation outline, he started designing presentation visuals. In sentence c), we also need to put a comma, to separate the prepositional clause from the rest of the sentence - On my desk, between the paperweight and the clock, you'll find the form you need. In sentence e), we should also use a comma - Between sessions, the conference participants visited the cafeteria. Sentences d and f are the only sentences that use the correct punctuation. Moreover, in sentence b), there is no need to use a comma to separate the subject from the predicate. The subject in this sentence is a gerund phrase 'introducing speakers before presentations'. The correct version of the sentence is - Introducing speakers before presentations is always a challenge.