(February 2013) Durham tubes are used in microbiology to detect production of gas by microorganisms. They are simply smaller test tubes inserted upside down in another test tube. This small tube is initially filled with the solution in which the microorganism is to be grown.
A compound predicate is two or more simple predicates joined by a conjunction that indicate actions by the same subject. Example : Bill picked up the mail and walked the dog.. Bill is the subject for both verbs.
Defining a Compound Verb. A compound verb is used when two verbs are needed to fully explain the action taken by the subject. There are four types of compound verbs: 1  A prepositional verb-When a preposition (such as in) combines with a verb (such as believe) to form a new verb. 2  Example: believe in.