Hard的近义词有:
difficult，firm， solid
It must be very difficult at sea， too .海上的日子想必也很不好过吧。
Doing so may be difficult in practice .在实践中这样做可能会有困难。
It is difficult to obtain reliable evidence .这很难取得可靠的凭据。
The contact resistance is difficult to measure .接触阻力很难测量。
The book is too difficult for me to read .这本书太艰深，我读不下去。
