The correct answer is A. MEK inhibitor.

Plexiform neurofibromas occur in neurofibromatosis. Selumetinib is a mitogen-activated protein kinase (MEK) inhibitor approved for use in patients age 2 years or older, for inoperable symptomatic plexiform neurofibromas.

mTOR inhibitors, such as Sirolimus, are used in the topical treatment of angiofibromas with tuberous sclerosis. BRAF inhibitors, such as vemurafenib, shrink or slow the growth of metastatic melanoma in people whose tumors have a BRAF mutation. VEGF inhibitors, such as bevacizumab, are used for several cancers. PD-1 inhibitors, such as Pembrolizumab, are used for several cancers, including melanoma.

References:

1. Baldo F, Grasso AG, Wiel LC, et al. Selumetinib in the treatment of symptomatic intractable plexiform neurofibromas in neurofibromatosis type 1: a prospective case series with emphasis on side effects. Pediatric Drugs. 2020;22(4):417-423. URL: https://pubmed.ncbi.nlm.nih.gov/32533336/

2. Gross AM, Wolters PL, Dombi E, et al. Selumetinib in children with inoperable plexiform neurofibromas. N Engl J Med. 2020;382:1430-1442. URL: https://pubmed.ncbi.nlm.nih.gov/32187457/