Species that have many offspring at one time are usually:

a. r-selected

b. K-selected

c. both r- and K-selected

d. not selected

While reproductive strategies are significant in life histories, they ignore important issues like as limited resources and competition. The management of population growth by these parameters can be used to establish the concept of K-selected vs r-selected species, which is a classic concept in population biology.

The idea refers to a species' reproductive tactics, environment, and behavior, particularly in terms of resource acquisition and child care. It also takes into account aspects like life expectancy and survival. Although the categories are truly two extremes of a continuum, population biologists have divided species into two main categories: K-selected and r-selected.

The population size of k-selected species grows exponentially until the niche's carrying capacity is reached. To facilitate appropriate embryological development, these species produce a few large-sized progenies and have extended gestation periods.

It is definitely not both r-selected or k-selected.

r-selected species are those that seek out sparsely populated ecological niches in order to exploit them and produce a large number of small-sized progeny with reduced survival rates due to short gestation periods and early maturity.

Thus, the correct answer is option (a).