1.if you -------more about giving first aid,you------us had

1.if you _______more about giving first aid,you______us had known,could have helped2.Never _____such an animal as Jim described after his coming back from the New Zealand.have i heard 还是 did i hear,还是had i heard问:1中had known是根据could have helped 往前推一个时态得出来的.那么在2中,是不是也可以用这种方法,把described往前推一个时态,得出 had i heard..为什么?