When prepositional phrase is placed first, make sure you identify the complete subject: very often compound subjects (two singular nouns joined by "and") will be used in this construction, which often appears at the end of the Error-Identification section. In such cases, a singular verb will incorrectly replace a plural verb.
Ex: Along the Loup Canal in Nebraska extends (extend) a park and lake owned an operated by the Loup power district.
-It is also permissible to use both what and whether as subjects (e.g. "Whether dogs are capable of experiencing complex emotions is a subject of much debate among experts."); both are singular.
-Do NOT use would have in a clause that begins with if:
If he would have arrived (had arrived) at 5pm, I would have been very happy.
G. The Subjunctive
The subjunctive is tested infrequently but does appear from time to time. It involves expressions of suggestion and necessity. The main change in the present subjunctive comes in the third person singular form of the verb:
Indicative (normal): He arrives home at 5pm.
Subjunctive: It is necessary that he arrive home at 5pm.
The past subjunctive involves hypothetical circumstances; it includes the verb were, regardless of whether the subject is singular or plural.
If he were to arrive at 5pm, I would be very happy.
Very often these kinds of questions also double as word pair questions (see list below).
When faulty comparison questions appear in Fixing Sentences, they will typically be fixed with the phrases that of (singular) or those of (plural)
Hint: Look for the phrase "as a + profession" (actor, physicist, entomologist...)
Who is for people, which/that is for things. In Error-IDs, which is typically used incorrectly to refer to people; who is not used to refer to things.
Incorrect: The book being (was) banned from a number of schools because it was so controversial.
2) Missing main verb
Look for classic "noun + of + noun" structure