I have no hesitation in recommending John

【問題】
I have no hesitation in recommending John Simpson, __________ has been a most reliable and hardworking employee.

【選択肢】
1.　whom
http://jibun.atmarkit.co.jp/scenter/ittrain/93_20060531_a1.html

2.　who
http://jibun.atmarkit.co.jp/scenter/ittrain/93_20060531_a2.html

3.　which
http://jibun.atmarkit.co.jp/scenter/ittrain/93_20060531_a3.html

4.　whose
http://jibun.atmarkit.co.jp/scenter/ittrain/93_20060531_a4.html

問題提供：リアル・イングリッシュ・ブロードバンド株式会社
http://jibun.atmarkit.co.jp/misc/ct.php?id=TR56_RE1
No.09320060531