Perplexing sentences

1- We .......the plants by the time you arrive home. You will find nobody there.

a) will be watering b) will have watered c) will water

2- My mother made me a cake . It .......of lemon.

a) tasted b) was tasting c) had tasted

3- I don't know from.......Tom bought this mobile.

a) where b) which c) that

4- September, .......the school year starts, is a hot month in our city.

a) on which b) which is when c) in when

5- My elder brother arrived home at 12 a.m.. .......I had already gone to bed.

a) by which b) on which c) to which

6- Half the main team........injured.

a) is b) are c) has

My answers

1- will have watered (My friend says the correct answer is 'will be watering'; however, I think the meaning of this sentence is not clear)

2- tasted

3- from where ( Do we use a preposition before 'where'?)

4- which is when ( I hope you will explain this structure to me)

5- by which

6- are