2.  A number of innovative developments (has, have) been made in the multi-component injection molding process in recent years.

3.  The number of takes singular verb while A number of takes a plural verb.

4.  A gas channel design 【 that (guides, guide) the gas flow to the desired locations 】 (is, are) one of the key factors that determine a successful application.

5.  The delay time along with gas injection points (is, are) important in producing injection-molded parts of quality.

6.  Expressions such as as well as, in addition to, along with, accompanied by and with should not confuse the reader into thinking that the sentence has a compound subject and, therefore, should have a plural verb.  The verb in this sentence should be singular since the subject, The delay time, is singular in form.

7.  Neither the processing parameters nor the amount of polymer melt injection solely (determine, determines) a successful gas channel design.

8.  The verb in the sentence is singular in form since the amount of polymer injection, not the processing parameters, is the closest to the verb.

9.  【 To select the number and locations of gas injection points 】 and 【 to determine the amount of polymer melt injection 】 (is, are) essential to a successful application.

10.  A compound subject, To select the number and locations of gas injection points and to determine the amount of polymer melt injection, takes a plural verb.

11.  Ergonomics (aim, aims) to integrate worker comfort and productivity.

12.  (Original) Each of the factors contributes to a successful design.  (Revised) Each factor contributes to a successful design.

13.  (Revised) The simulation 【 in which the polymer melt flow occurs in thin cavities 】 provides accurate predictions.

14.  Writers should be careful not to choose the wrong verb form by becoming distracted by words or phrases between the subject and the verb.

15.  【 Establishing a general model or empirical formula in addition to describing the thickness variation of the skin melt that exists between the gas/melt interference and the cavity wall 】 appears to be necessary for further development.

16.  The number of gas injection points is important in producing quality injection-modeled parts.

17.  The majority of factors heavily influence product performance.

18.  The verb should be plural in this sentence since the noun refers to individual factors.

19.  【 Accurately determining the interface shape of a bubble nose 】 and 【 properly selecting the film thickness 】 are of primary concern.