Agricultural scientists continue to search for a strain of wheat that is
hardy, disease-resistant and yields more grain per acre.
Issues in this question - We don't know which elements are parallel in the list. First identify if there are two lists of parallelism or three elements in parallel.
There can be two list of parallelism - hardy, diseases -resistant and that is and that yields or hardy, resists diseases and yields.
Now, in this question, we have two lists of parallelism. identify this by checking two things - parallel lists should a)logically and b)grammatically parallel.
Logically, three elements can be parallel but these elements hardy, diseases -resistant are adjectives whereas yields more grain is a clause so that is not necessarily an error.
Grammatically, if you would see substitute "is" with every element of list and see if it makes sense.
is hardy, is diseases -resistant and
is yields more grain per acre.So, there are two lists. If that is the case, then we need a) "and" between hardy and diseases -resistant & b) that before yields to show two requirements.
Remove one parallel list - So, remove A, E. E can also be removed because it has verb-ing can't be parallel to adjectives. Eliminate D because that changes the meaning. Now, B and C are left.
In B, apply is before resists diseases which is incorrect. So, C is the answer.
A.hardy, disease-resistant and yields - B.hardy, resists disease, and that yields
C.hardy and disease-resistant and that yields
D.hardy and resist disease, yielding
E.hardy, disease-resistant, and yielding