Answer Happy

Although hydrogen gas has about half the density of helium gas, and therefore it can be used to lift heavier loads than a hollum-filed balloon of the same volumo, we often don't use it when lifting humans due to select all that apply) a hydrogen gas is very flamable b. hellum gas is cheap, plentiful, and oney to obtain on Earth c. hydrogen gas is for too hard to contain inside a balloon d. hydrogen gas is very rare and hard to come by hydrogen gas has a very nasty smell