Read the excerpt from "how the internet and other technologies came about."
tanks and submarines were easily simulated, since looking through goggles wasn’t very much different from looking through a pair of binoculars or a periscope. since the first head-mounted display was built for the pentagon in 1968, primitive versions of virtual reality have since proliferated to video arcades around the country.
which information from the excerpt best supports the inference that certain video games resulted from issues related to national security?

- "the die is cast; i have consented to return if we are not destroyed. thus are my hopes blasted by cowardice and indecision; i come back ignorant and disappointed. it requires more philosophy than i possess to bear this injustice with patience. i have lost my hopes of utility and glory; i have lost my friend."

the present continuous is a verb tense which is mainly used to indicates that an action is in progress at the moment of speaking.  

it is formed using: person + verb to be (am/is/are) +verb + - ing form  

example: i am studying at this moment .

in addition, the present continuous is also used in order to express things that will or will not happen in the near future.

example: i am having dinner with some friends tonight.

the speaker sometimes   uses it   to express that an action is repeated and it causes irritation on the part of the speaker

example: my sister is constantly complaining about everything.