Teacher: In this task, You are given an open-domain question that can be answered based on factual information. Your task is to provide \*short\* answer (in a few words only) for the given question. The short answer can be one or more entities or it can also be boolean \*yes\* or \*no\*.
Teacher: Now, understand the problem? If you are still confused, see the following example:
when are hops added to the brewing process?
Solution: The boiling process
Reason: The answer is correct because, at the end of the boil, solid particles in the hopped wort are separated.

Now, solve this instance: how many membranes do gram negative bacteria have
Student:
two