Answer:
Quota sampling
Step-by-step explanation:
Quota Sampling is a non-probability sampling method in which the population is divided in mutually exclusive subgroups and the items from each of the subgroups are selected based on a proportion.
In this example the households were divided into two subgroups: single-person households and husband-wife households (it is clear that this subgroups are mutually exclusive). Then, since 40% of all households are single-person and 60% are husband-wife, the researcher ask interviewers to collect information based on this proportion, therefore, 40% of the interviews will be done with single-person households and 60% with husband-wife households. Thus, these interviews are done based on a proportion.
We can see that the example meets all the requirements for quota sampling and thus, it's an example of this type of sampling.