英语句子改错

1-----The Johnsons have just moved into a large house and are planning to buy many new pieces of furniture.
原因： 家具Furniture不可数名词

2-----By 2050.scientists will surely have discovered a cure for AIDS.
原因： surly与must语意重复。 此句应用将来完成时， 故原句时态不对。

3-----In modern age,electronics is developing very fast.
或者是 In recent years,electronics have been developing very fast.
时态不对，原句将现在进行时的提示语（in modern age）与现在完成时混用了。

4------Do they always wave you goodbye in this informal way?
wave sb goodbye是固定搭配， 中间没有介词to

5------They began a new course yesterday.
since是完成时的提示语， 此句应用一般过去式，since多余

6------Mary is the better player of the two.
两者之中相比较好的用better， 三者用best