Answer:
All the factors listed in the question are related to low GDP except for low labor costs:
an economy based on agriculture
Economies based on agriculture tend to have a low GDP, because agriculture usually produces less output than industry and services.
an economy based on a few industries
Economies lacking complexity, most of the time (not always) have a low GDP. An economy based on a few industries is not only vulnerable to shocks, but also likely to be unproductive.
a low standard of living
A low standard of living is directly related to GDP, more specifically, to GDP Per Capita. This is a statistical relationship that has been established by countless economic studies.
a lack of infrastructure
A country that lacks physical infraestructure will usually have a low GDP, because infraestructure is needed to both the production and delivery of goods and services.