Visit visa canada..immigration officer letter

Hi,
Recently my father and mother had applied for canadian visitor visa to meet my uncle and tourism. My parents are living in UK on Tier 2 Inter company transfer visa and they applied from London through online cic account.
Now Canadian immigration officer have sent a letter demanding an answer on "US enforcement history (inadmissibility)" Although my father or any of us never got refused an entry or visa of USA.
My parents and family applied for USA visa once and got 5 years visa, we never over stayed or did any illegal things.
Following are the content of letter:

Dear Name:
This refers to your application for a Temporary Resident Visa.
Your application and all of the documents you submitted in support of it have been reviewed and it appears that you may not meet the requirements for immigration to Canada.
Subsection 11(1) of the Immigration and Refugee Protection Act (IRPA) provides that a foreign national must, before entering Canada, apply to an officer for a visa or any other document required by the Immigration and Refugee Protection Regulations. The visa or document shall be issued if, following an examination, the officer is satisfied that the foreign national is not inadmissible and meets the requirements of the Act.
I have concerns that you have not fulfilled the requirement put upon you by subsection 16(1) of the Immigration and Refugee Protection Act which states:
16(1) A person who makes an application must answer truthfully all questions put to them for the purpose of the examination and must produce a visa and all relevant evidence and documents that the officer reasonable requires.
Specifically, I have concerns that you failed to disclose prior US enforcement history (inadmissibility).
Please note that if it is found that you have engaged in misrepresentation in submitting your application for a Temporary Resident Visa, you may be found to be inadmissible under section 40(1)(a) of the Immigration and Refugee Protection Act. A finding of such inadmissibility would render you inadmissible to Canada for a period of five years according to section 40(2)(a):
40(1) A permanent resident or a foreign national is inadmissible for misrepresentation (a) for directly or indirectly misrepresenting or withholding material facts relating to a relevant matter that induces or could induce an error in the administration of this Act
40(2) The following provisions govern subsection (1):
(a) the permanent resident or the foreign national continues to be inadmissible for misrepresentation for a period of five years following, in the case of a determination outside Canada, a final determination of inadmissibility under subsection (1) or, in the case of determination in Canada, the date the removal order is enforced.
I would like to provide you with the opportunity to respond to this information. You will have 10 days from the date of this letter to submit additional information in this regard. Please respond using the address at the top of this letter and clearly indicate your file number for all correspondence.
If you do not respond to this request within 10 days, your application will be assessed based on the information currently on file and may result in the refusal of your application.
Sincerely, Immigration Officer

Please let me know what should we do to satisfy immigration officer.

I am also looking for job opportunity in Canada. But don't know the procedure. What should I do now?