Use past tenses, present perfect or past perfect tenses to complete these sentences

three clients since the morning.(contact)
i couldn't help you. problems.(not understand)
does he know about yet? (tell)
bill admitted that he catalogue to the agency. (not send)
as soon as i the message, i my house. (get, leave)
while maggie new jumper, jill and i (knit, read).

she has contacted three clients since the morning. (contact)

i couldn't help you. i didn't understand your problems. (not understand)

does he know about it? have you told him yet? (tell)

bill admitted that he hadn't sent the catalogue to the agency. (not send)

as soon as i got the message, i left my house. (get, leave)

while maggie was knitting a new jumper, jill and i were reading. (knit, read).

1)the .lily-of-the-valley.. is a beautiful spring flower.

2)there are a lot of..islands. in the pacific ocean.

3)the baikal is the ..deepest. lake in the world.

4)masha spent her holidays on the black sea .coast..

5)moscow is a very ..large. city.

6)the mississippi is a .large.. river, it is the ..largest. river in the usa.

7)the mississippi .flows..south.

8)the urals is a famous .chain.. of mountains.

9)is the volga a .deep.. river.

10)there are four .parts.. in great britan.  they are england,wales,scotland and northern ireland.

11)are there any .plains.. in europe?

12)washington, d.c. lies.. on the potomac river.

13)the forest was .stretching.. to the east.

1. can

2. could

3. were able 

4. can

5. are able

6. can

(не уверенна)