Problem $1$: $(6$ points$)$ Consider the portion of a flow tube shown in the figure. Point $1$ and point $2$ are at the same height. An ideal fluid enters the flow tube at point $1$ and moves steadily toward point $2.$ If the cross section of the flow tube at point $1$ is greater than that at point $2,$ then the pressure at point $2$ is

$[$a$]$ lower than the pressure at point $1.$

$[$b$]$ equal to the pressure at point $1.$

$$ cc higher than the pressure at point $1.$

$[$d$]$ is impossible to be determined.