Option pricing theory questions???

Sir, what is the logic behind the sentence, used in many past xam answers, the equity provided by lenders is considered as a calll option written by the lenders…
These option pricing Qusetions always confuse me i dont know how to answer such theoretical parts…
FOR example i didn get anything dat is written in the following answer part copied frm past xam…i will b garteful to u if u explain it in simple words or explain the logic behind it..
“Inconsidering the value of this business you should note that the company has a very high level of gearing and that this
imparts additional value to you through your possession of limited liability. The value quoted above is a fair value of the
business in your hands based upon the expected value of the future cash flows of the enterprise accruing to you. This is the
equivalent of the fair value of the firm’s assets less its outstanding liabilities including its debt.
However, the possession of limited liability gives you an effective call option on the value of the business against the lenders
in that in extremis, if the value of your equity fell to zero, you could liquidate and the lenders would bear any loss. As
shareholders you have the potential of ‘upside’ gains but are not exposed to downside losses. This advantage on the upside
means that your limited liability represents an asymmetric claim on the business and this is a valuable right which is
particularly important during the growth stage of a business.
This additional value is termed its ‘structural value’ and it is at its maximum when the value of the assets of the firm
approximate to the value of the outstanding debt but it diminishes as that differential widens. A structural valuation of your
firm could be undertaken but would need estimates of the volatility of the returns generated by the firm’s assets and the length
of time which the debt will be held to maturity.”