'hard core' vs 'hard up' vs 'hard sell' vs 'hard court'

[Wisemarie]

English Language Tests, Intermediate level

ESL/EFL Test #189 "Idioms with the word 'hard'", question 1

Poor people in Australia who are ......... for cash may seek financial assistance from the Salvation Army.

(a) hard core
(b) hard up
(c) hard sell
(d) hard court

English Language Tests, Intermediate level

ESL/EFL Test #189 "Idioms with the word 'hard'", answer 1

Poor people in Australia who are hard up for cash may seek financial assistance from the Salvation Army.

Correct answer: (b) hard up
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my answer is "a" because i quite don't know how to differentiate the meaning of the words from the given selection of answers. please explain. thanks.

[Kitosdad]

(a) hard core ........ pornography or a militant, bigoted group.
(b) hard up ....... little or no money.
(c) hard sell.......to sell by pressurising people.
(d) hard court ..... a tennis playground.
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Englishman living in Germany.