How to clear drop down list contents based on contents of another cell

[james_007_gr]

Hello

I am using open office calc (apache) and in my document
I have a number of dropdown lists e.g dropdown list 1 has the following entries:
Not Selected
Yes
No

In another worksheet of the same document I ask various questions (say to some sales people) e.g
(in cell A6):
Q1) Would you like your machine to have heating?
The sales person can then choose (say in cell B6) any of the above mentioned (e.g Not selected or Yes or No)

Now If the next question is not relevant to the question answered before
ideally I would like to be able to make invisible the question and also its associated drop down list.
e.g Question in cell A7:
Q2) Choose Heating Brand (Dropdown list 2 options (e.g in B7) are: Brand A; Brand B; Brand C etc)


I have found a way to make contents of A7 invisible using IF then else statements
e.g =IF(B6="Yes";"Choose Heating Brand";"")
However B7 would be expecting from the sales person an answear e.g
Brand A; Brand B; Brand C

Idealy I am looking for a way to clear the drop down list contents since Q2 been invisible.
I am looking for the easiest solution, hopefully not involving macros (if possible) since
I am new into excel programming however I have programming skills in C/C++, ladder, etc.

Any answer/suggestion/code could even be in Microsoft excel 2010 or open office 365

Thanks for your time and help