How many known stis exist today?

a. less than 5
b. less than 10
c. less than 20
d. more than 20

There is more than 20 STIs exist today, Actually The number of STIs (sexually transmitted infections) will vary depending on what is counted as an STI and whether sexually transmissible infections are counted. The Medical Institute uses a list of STIs that is adapted from chapter headings in a standard STI textbook. Some of them are:
a. Bacterial
b. Ectoparasitic
c. Protozoal
d. Viral
 
In above types viral has more and severe sub-forms which is well known today society.
 
cytomegalovirus
Epstein Barr virus
hepatitis A
hepatitis B
hepatitis C
hepaptitis D
herpes simplex virus (HSV-1 and HSV-2)
human immunodeficiency virus (HIV)
human papillomavirus (HPV)
human T-cell lymphotropic virus (HTLV-1)
molluscum contagiosum.
These are brief explanation of above question

There is a lot of things if u give me the list i can