1 subway

2 metro

1 subway station

1 factory

2 classifier: 家 jiā

3 classifier: 座 zuò

1 steel

1 piano

2 classifier: 架 jià

3 classifier: 台 tái

1 one can't function properly on an empty stomach (idiom)

2 an empty sack cannot stand upright

1 If you work at it hard enough, you can grind an iron bar into a needle.

2 cf idiom 磨杵成針|磨杵成针, to grind an iron bar down to a fine needle (idiom); fig. to persevere in a difficult task

3 to study diligently

1 lit. to hate iron for not becoming steel

2 to feel resentful towards sb for failing to meet expectations and impatient to see improvement (idiom)

1 lit. not an inch of steel (idiom); unarmed and defenseless

1 lit. to chop the nail and slice the iron (idiom)

2 fig. resolute and decisive

3 unhesitating

4 categorical