The company was

[figs]

The company was not even publicly traded until 1968, when the owner and founder sold it to David P. Markham, a private investor, who took the company public and established a long and generous policy of stock options for valued employees.

A.who took the company public and established a long and generous policy of stock options for

B.who, taking the company public, established a long and generous policy of stock options to

C.who, when he took the company public, established a long and generous policy of stock options to

D.who had taken the company public, establishing a long and generous policy of stock options to

E.taking the company public and establishing a long and generous policy of stock options for

[matterover]

stock options for employees is preferred over stock options to.
leaves us with A and E.

E is ambiguous in the sense

when the owner and founder sold it to David P. Markham, a private investor,
taking the company public and establishing a long and generous policy of stock options for

here it is not sure who took the company public, whether the owner or David.
owner sold to David, taking the company public....indicates that his selling resulted in taking the company public.

[cramya]

A

Since it deals with the past simple past is sufficient. Who unambigously refers to David P. Markham No need for past perfect tense especially for the second action(taking the company public)

E sounds like its happenning now which is not what the original sentence tried to convey.

Also E conveys the meaning that the compnay was sold to some one who is taking and establishing certain things which doesn't make much sense

[rs2010]

One more hand up for A.
BCD are workdy and awkward.

E distorts meaning by saying founder taking & establishing it.

[figs]

oa:a