Option(B) is correct
There are two main problems with the original sentence.
(1) The subject (Dr. Martin A. Tidball) is singular and does not agree with the verb (are), which is plural.
(2) The three actions Dr. Tidball is working on are not listed in parallel form. The correct listing would have each action as a present participle: uncovering...discovering...enhancing
Note: You could also write the sentence in a parallel fashion with infinitives: is working hard to uncover the mysteries of glucose uptake, discover new details concerning active ATP transport, and enhance facilitated diffusion using a drug.
A. the subject (Dr. Martin A. Tidball, which is singular) does not agree with the verb (are, which is plural); the three actions Dr. Tidball is working on are not listed in parallel form (i.e., the phrase uncovering...a discovery...and a drug to enhance is not parallel)
B. the subject (Dr. Martin A. Tidball, which is singular) agrees with the verb (is, which is singular); the three actions Dr. Tidball is working on are listed in parallel form (i.e., the phrase uncovering...discovering...and enhancing is parallel)
C. the three actions Dr. Tidball is working on are not listed in parallel form (i.e., the phrase to uncover...[to] discover...and enhancing is not parallel)
D. the subject (Dr. Martin A. Tidball, which is singular) does not agree with the verb (are, which is plural)
E. the subject (Dr. Martin A. Tidball, which is singular) does not agree with the verb (are, which is plural)