Why are angiosperms better able to produce offspring than other plants?

Angiosperms are the most successful plant group is because they have pollens and flowers/fruits. The flowers are able to attract insects and this allows better transportation of pollen. Also, animals and insects may eat the seeds, and that would also be good transportation of the seed because the seed is usually excreted. 
Angiosperms also go through something called double fertilization, which helps the plant 
They have a lot less cells than gymnosperm 
MOst importantly they have vessels that can escalate their growth

Answer the use of flood plains and irrigation;

The us is first  the  u.s. economy  remains the  largest in the world  in terms of nominal  gdp. however, the  u.s. economy  loses its spot as the number one  economy  to china when  measured  in terms of  gdp  based on ppp. in these terms, china's  gdp  is $23.19 trillion exceeds the  u.s. gdp  of $19.42 trillion